TJ 




Class JTlZXL 
Book -S ^5 



Copyright N°_ 



COPYRIGHT DEPOSIT. 




REYNOLDS COMBINED VERTICAL 
POWER CYLINDERS, 44x88x60. 



AND HORIZONTAL ENGINE 12,000 HORSE 
BUILT BY ALLIS-CHALMERS COMPANY. 



Twentieth Century Hand-Book 

FOR 

Steam Engineers and Electricians 

WITH QUESTIONS AND ANSWERS 



A PRACTICAL NONTECHNICAL TREATISE 

On the Care and Management of Steam Engines, Boilers and Dynamos. 
With Full Instructions in Regard to the Intelligent Management of all 
Classes of Steam Engines, Making Evaporation Tests on Boilers, 
Hydraulics for Engineers, the Adjustment of the Slide Valve, Corliss 
Valve, etc., Fully Described and Illustrated, together with the Applica- 
tion of the Indicator and Diagram Analysis. All Problems are Solved 
in Plain Figures, thus Enabling the Man of Limited Education to readily 
comprehend their meaning. 



New 1905 Revised and Enlarged Edition 

TO WHICH IS ADDED FULL AND COMPLETE CHAPTERS 
ON THE STRENGTH OF BOILERS, MECHANICAL 
STOKERS, AND CLEAR DESCRIPTIONS OF 
THE STEAM TURBINE, ITS CONSTRUC- 
TION AND MANAGEMENT 

By C. F. SWINGLE, M.E. 



ELECTRICAL DIVISION 

Containing only such information as Steam Engineers should know 

to successfully and economically run or manage an electrical plant 

BY 

HENRY C. HORSTMANN & VICTOR H. TOUSLEY 



ILLUSTRATED 




CHICAGO 

FREDERICK J. DRAKE & CO., PUBLISHERS 

1905 



uBRARY o! 3QNGRESS 
fwu Copies rtecwveU 

CQcyn^nt tntfjf 
CUCSS « XXc. Not 

//37/ 2^ 

COPY 8. 




COPYRIGHT, 1905 

BY 

FREDERICK J. DRAKE & COMPANY 

CHICAGO, U. S. A. 



, ' 



t 



1 







TYPOGRAPHY BY 

MARSH, AITKEN & CURTIS COMPANY, CHICAGO 



LIST OF ILLUSTRATIONS 



PART I STEAM ENGINEERING 



American Thompson indicator, 

176. 
Amsler's polar planimeter, 263. 
Ashcroft steam gauge, 36. 

Baragwanath closed heater, 53. 

Baragwanath open heater, 55. 

Babcock and Wilcox water 
tube boiler, 16. 

Berryman closed heater, 57. 

Baragwanath siphon conden- 
ser, 272. 

Coffin averager or planimeter, 

261. 
Crosby indicator, sectional view, 

170. 
Crosby indicator, with reducing 

wheel, 183. 
Cross compound Allis-Chalmers 

engine, 266. 
Center oiler for crank pin, 279. 

Davis belt-driven feed pump, 48. 
Differential valve for Davis 

pump, 47-49. 
Detroit lubricator, 277. 



Green's fuel economizer- 
construction, 94. 



-under 



Hamilton Corliss engine— cro 

compound, 268. 
Horizontal boiler setting, 12. 
Heine water tube boiler, 14. 
Hot water thermometer, 59. 



Inside view of pop valve, 41 „ 

Knowles jet condenser, 269. 

Lahman shaking grate, 67. 

Martin rocking grate, 68. 
Marsh steam pump, 50. 
Metropolitan injector, 52. 
McClave shaking grate, 33-35. 

Pop safety valve, 40. 
Pickering governor, 276. 
Penberthy injector — sectional 
view, 285. 

Schaefer and Budenberg steam 

gauge, 38. 
Sectional view of pressure gauge, 

37. 
Sectional view of Corliss cylinder 

and valve chests, 158. 
Shaft governor, 281. 

Tandem compound Buckeye 

engine, 267. 
U. S. Automatic injector, 51. 
Wickes vertical water tube 

boiler, 13. 
Worthington duplex feed pump, 

49. 
Worthington surface condenser, 

271. 



INDEX 



PART I STEAM ENGINEERING 



Absolute pressure, 190. 
Absolute back pressure, 191. 
Absolute zero, 193. 
Action of slide valve, 134-139. 
Adiabatic curve, 194-252-254. 
Adjustable cut-off, 145-203. 
Admission, 1C8. 
Admission line, 208. 
Adjustment of governor, 164- 
165. 

Air — 

Composition of, 91. 

Cubic feet per lb. of coal 

burned, 70-93. 
Leaks in boiler settings, 33-34. 
How to admit to furnace, 

70-71. 

Angular Advance — 

Necessity of, 136. 

Effect of decreasing, 144. 

Effect of increasing, 148-149. 

Definition of, 201. 
Analysis of coal, 92. 
Apparatus for making tests, 

118-120. 

Area — 

Of circles, 204-205. 

Of fire box, 61. 

Of grate surface, 121. 

Of heating surfaoe, 61. 

Of safety valve, 39. 

Of segments, 22. 

Sectional of braces, 21-22-23. 

Ash— 

Dry, 123. 

Removal of, 29-121 

Weight of, 127. 
Atoms, 106-107. 
Atmospheric line, 186. 
Automatic stoker, 94. 
Automatic cut-off, 202. 



Back pressure, 190, 
Blow-off- 
Pipes, 45-47. 

Cock, 46. 

Surface, 47. 
Boiler — 

Air leaks in brick work, 34. 

Back arches, 29-31-34. 

Bridge Walls, 28. 

Bracing, rules for, 22-23-24. 

Bursting pressure, 18. 

Cleaning, 71-73. 

Combustion chamber, 29. 

Contraction of plates, 43. 

Expansion of plates, 44. 

Factor of safety, 21. 

Force tending to rupture, 19, 

Flue cvlindrical, 11.' 

Grate surface, 32-33. 

Horse power of, 131. 

How to prevent alternate ex- 
pansion and contraction, 
72-73. 

Incrustation, 104. 

Insulation, 33-34. 

Inspection, 73-74. 

Operation of, 66. 

Plain cylinder, 11. 

Return tubular, 12. 

Rivets, 15-16. 

Settings, 27. 

Set in battery, 28-122. 

Shell material, 14-15. 

Types of, 11. 

Tubes, renewing of, 74. 

Water tube, i3. 

What causes alternate ex- 
pansion and contraction. 73. 
Boyle's law, 194. 
Box valve, 157. 
Brumbo pulley, 181. 
British thermal unit, 98-99. 
Buck stays, 31-32. 



Ill 



Calorimeter, 124. 

Chimney draft, 124. 

Circulating system, 47. 

Cleaning fires, 67. 

Cleaning flues, 71-72. 

Clearance, 193-236-245-246. 

Combustion, 91-94. 

Coal- 
Analysis of, 92. 
Moisture in, 124. 

Composition of matter, 106. 

Connecting steam gauge, 38. 

Connecting boiler to main head- 
er, 75-76. 

Corliss valves, 158-163. 

Corliss valve gear, 158-160. 

Condenser pressure, 191. 

Counter pressure, 260. 

Compression, 194-202-236-238. 

Condenser- 
Jet, 270. 
Surface, 270. 
Siphon, 271. 

Water required per H. P. per 
hour, 274-276. 

Curves — 

Adiabatic, 194-252-254. 
Compression, 236-238. 
Expansion, 194. 
Isothermal, 194-246-251. 
Theoretical expansion, 246- 
251. 

Cut-off- 
Automatic, 202. 
Adjustable, 203. 
At half stroke, 149. 
Equalizing, 212-226. 
FLxed, 202. 

- Of slide valve, 137-142. 

Cylinder condensation, 200. 

Dash pot, 162-165. 
Diagrams — 

From Corliss centennial en- 
gine, 232-235. 
From Hamilton Corliss en- 
gine, 235-236. 
From Buckeve engine, 208- 

216-218-226-227. 
From Bates vertical Corliss 
engine, 209-212. 



Diagrams— 

From Bullock horizontal Cor- 
liss engine, 213-216. 
From Atlas riding cut off 

engine, 218. 
From cross compound con- 
densing engine, 219-220. 
From Fishkill Corliss con- 
densing engine, 222-224. 
From vertical slide valve en- 
gine, 224-225. 
Friction, 260. 

Showing lines and curves, 207. 
Domes — 

Purpose of, 43 
Bracing, 24. 
Draft gauge, 125. 
Duplex Pump — 

How to set valves of, 81-82. 
How to operate with one 
water piston disabled, 82- 
83._ 
Dynamics, 195. 

Economy in fuel, 51-57. 
Economizers, 94. 
Eccentric — 

Adjustment of, 156-161. 

Definition of, 200. 

Position, 138-139-201. 

Rod, length of, 153-154. 

Throw, 201. 
Efficiency test, 122. 
Efficiency of plant, 197. 
Energy in one pound of coal, 

102.' 
Engine — 

Corliss, 158. 

Compound, 268. 

Compound, distribution of 
steam in cvlinders, 221-222. 

Changing of speed, 287-288. 

Efficiency of, 196-197. 

Four valve, 157-159. 

How to place on center, 
150-153. 

Keying up, 281-282. 

Operation of, 266-288. 

Steam consumption of, 198- 
236-238-242. 

Single valve, 134. 



Equivalent evaporation, 127. 
Evaporation — 

Factor of, 128-129. 
Exhaust — 

Cramped, 225. 

Injector, 57-58. 

Heater, 53-54-55-57. 

Line, 208. 
Expansion curve, 194-208. 

Factor of safety, 20. 

Factor of evaporation, 128-129. 

Feed pipes, 43-45. 

Feed Pumps — 

Belt driven, 47. 

Best water valves for, 80. 

Double acting, 48. 

Selection of, 48-50. 
• Setting steam valves of du- 
plex pump, 81-82. 
Feed Water- 
Heating by exhaust steam, 
283-285. 

Proper supply of, 74-75. 

Quantity required, 49-51. 

Temperature of, 43. 

What to do if supply is cut 
off, 75. 
Feed Water Heaters — 

Closed, 53. 

Capacity of, 56-57. 

Economy of, 52. 

Live steam, 58. 

Open, 53. 
Fire tools, 68. 

Firing, proper method of, 69-71. 
Fire brick lining, 28-33. 
First law of thermo-dvnamics, 

194. 
First law of motion, 194-195 
Fixed cut-off, 202. 
Foaming, 76. 
Formula — 

For ascertaining friction loss 
in water pipes, 87. 

For decreasing speed of en- 
gine, 288. 

For double riveting, 20. 

For efficiency of boiler, 130. 

For estimating quantity of 
condensing water, 274. 



Formula — 

For finding bursting pres- 
sure, 20. 
For finding heating surface, 

62-64. 
For increasing speed of en- 
gine, 287. 
For per cent, of saving by 
use of exhaust heater, 56. 
For single riveting, 21. 
Force, definition of, 195. 
Friction of water in pipes, 

86-88. 
Fusible plugs, 40-42. 
Furnace temperature, 93. 

Gauges — 

Draft, 125. 

Steam, connecting, 38-39-40. 

Vacuum, 192. 
Gauge pressure, 190. 
Generation of steam, 107. 
Governor — 

Throttling, 202-276. 

Automatic cut-off, 276. 

Isochronol, 202-281. 
Grate Surface — 

Length and width of, 32. 

Ratio of to heating surface, 33. 

Ratio of to safety valve area, 
39-40. 

Square feet of, 121. 
Gridiron valve, 157. 

Hand firing, 95. 

Hand holes, reenforcing, 24. 

Heater — 

Closed, 53-57. 

Capacity of, 56. 

Live steam, 57. 

Open, 54-55. 

Economy of, 52. 
Heating Surface — 

Of horizontal boilers, 61. 

Of vertical fire box boilers, 61 . 
Heat — 

A form of energy, 96. 

External work of, 108. 

Internal work of, 108. 

Intensity of, 95. 

Latent, 102-103. 



Heat — 

Mechanical equivalent of, 99. 

Original source of, 97. 

Sensible, 99-101. 

Specific, 99. 

Theories regarding nature of 
95-96. 

Unit of,' 98-99. 
High speed engines, 157. 
Hook rod, adjusting length of, 

160-161. 
Horizontal boiler setting, 12. 
Horse Power — 

Definition of, 102-193. 

Constant, 197-228-230. 

Indicated, 193. 

Net, 194. 
Hot water thermometer, 58-59. 
Hydraulics, 83-87. 
Hydrogen, 91. 
Hyperbolic logarithms, 188. 

Internally fired boilers, 23. 
Initial pressure, 190. 
Injector — 

Care of, 286. 

Exhaust, 285. 

Live steam, 286. 

Principles of, 285-286. 
Indicator — 

By whom invented, 168. 

Care of, 185-223-224. 

Description of, 171-175. 

How to attach, 183-185. 

Principles of, 168-171. 

Spring, 172. 

Study of diagrams, 207-230. 

Taking diagrams, 186-187- 
188. 
Isochronol governor, 202-281. 

Joule's experiments with heat, 
97-98 

Latent heat, 102-103. 
Lap — 

Effect of increasing, 134- 
145-146. 

Inside, 135-144-201. 

How to measure, 154-155. 



Lap — 

Meaning of, 201. 

Of Corliss valves, 164. 

Outside, 135-141-201. 
Lead — 

Adjustments for, 156. 

Definition of, 201. 

Equalized, 156-164. 

Necessity of, 134. 

Of Corliss valves, 164. 
Logarithms, 197. 
Lubrication — 

Of crank pin, 279. 

Of guides, 278. 

Of pillow blocks, 280. 

Of piston, 277. 

Of valves, 277. 

Margin of safety, 13. 
Material for boilers, 14. 
Manholes, reenforcing, 24. 
Maximum theoretical duty of 

steam, 195. 
Measuring lap, 154. 
Measuring chimney draft, 124- 

125. 
Mean Effective Pressure — 

Definition of, 190. 

Figuring by ordinates, 255- 
259. 

Finding bv planimeter, 262- 
263. 

Rule for finding, 220-227. 
Mechanical equivalent of heat, 

98-99. 
Momentum, 195. 
Moisture — 

In steam, 123-124. 

In coal, 124. 
Mud-drums, 43. 

Obliquity of connecting rod, 

147. 
Operation of boilers, 65. 
Ordinates, 200-255-257. 
Outside lap, 146. 

Packing for feed pumps, 80. 
Pantograph, 182-183. 
Pendulum motion, 177-182. 



VI 



Piston — 

Clearance, 193. 

Displacement, 193. 

Speed, 193. 

Valve, 157. 
Placing engine on dead center, 

151-152. 
Planimeter, 262-263. 
Power — 

Calculations, 254-259. 

Definition of 194. 
Priming, 76. 

Questions — 

On boiler operation, 87-90. 
On boiler construction, 24- 

25-26. 
On boiler settings, 64-65. 
On combustion, 115-116. 
On definition of words, terms, 

and phrases, 204. 
On diagram analysis, 230- 

231-263-265. 
On engine operation, 288-290. 
On evaporation tests, 131— 

132. 
On indicator, 188-189. 
On valve setting, 166-167. 

Radius of eccentricity, 140-141. 
Ratio of expansion, 191. 
Reevaporation, 251-252. 
Reducing mechanism, 176-183. 
Relative positions of crank pin 

and eccentric, 139. 
Release, 142. 

Rocker arm, how to adjust, 150. 
Rules — 

For ascertaining required size 

of feed pump, 50-51. 
For calculations in hydraulics, 

83-86. 
For finding piston speed of 

pumps, 83-84. 
For finding strength of solid 

plate, 15. 
For finding strength of rivets, 

16 
For finding strength of riveted 
seams, 15. 



Rules — 

For finding area of segment 

of circle, 22. 
For finding velocity of flow 

of water in pipes, 84-85. 
For finding weight of water 

discharged per second, 85- 

86. 
For finding initial pressure, 

220. 
For finding mean forward 

pressure, 220. 
For finding mean effective 

pressure, 220-227-228. 
For finding terminal pressure, 

242. 
For finding indicated horse 

power, 228. 
For safety valve calculations, 

78-79. 
For spacing braces, 23. 

Safe working pressure, 15. 
Safety Valve- 
How to keep in good working 
order, 80. 

Problems, computation of, 
78-79. 

U. S. marine rule for, 77. 
Sensible heat, 99-101. 
Shaking grates, 67-68. 
Smoke prevention, 94-95. 
Specific heat, 99. 
Steam line, 209. 

Strength of riveted seams, 15. 
Strength of solid plate, 15. 
Strength of rivets, 15. 
Steam — 

Consumption per H. P. per 
hour, 198-236-238-242. 

Clearance, 193. 

Density of, 109. 

Dry, 108. 

Gaseous nature of, 107. 

In its relation to the engine, 
109. 

Efficiency of, 195-196. 

Generation of, 106. 

Method of testing drvness of 
109-124. 

Nature of, 107. 



Steam — 

Percentage of moisture in, 
123-124. 

Physical properties of, 110- 
114. 

Relative volume of, 109-110. 

Saturated, 107. 

Superheated, 107-108. 

Temperature of, 107 

Total heat of, 108. 

Volume of, 109. 

Wet, 108. 
Surface blow off, 46-47. 
Tables- 
Analysis of coal, 92. 
Areas and circumferences of 
circles, 204-205. 

Constants for areas of seg- 
ments, 22. 

Factors of evaporation, 129. 

Constants for steam consump- 
tion per I. H. P. per 
hour, 228. 

Hyperbolic logarithms, 199. 

Lap and lead of Corliss 
valves, 164. 

Physical properties of steam, 
110-114. 

Specific heat, 99. 

Weight of water, 105. 
Temperature — 

Of escaping gases, 93. 

Of feed water, 74-123. 

Of furnace, 93. 
Tensile strength, 14. 
Terminal pressure, 190-242. 
Tests- 
Evaporation, object of, 117. 

Preparing for, 119-121. 

Duration of, 123. 

Closing of, 124. 

Record of, 127. 

Provisions for, 58-60. 

Tanks for, 59-60. 

For efficiency of boiler and 
furnace, 126. 

For efficiency of boiler, 126. 
Thermo dynamics, first law of, 

96-97-194. 
Theoretical clearance, 243-246. 
Three-way cock, 175. 



Throttling governor, 202-276. 
Tie rods — 

For boiler walls, 31-32. 

Transverse, where to locate, 
32. 
Total heat of evaporation, 102- 

103. 
Travel of valve, 137. 
Triple riveted butt joints, 18. 

Unit of work, 194. 

Vacuum, 192. 
Valve — 

Adjustment of travel, 156. 

Corliss, how to adjust, 162. 

Diagrams, 145-148. 

Decreasing travel of, 145. 

Gear of Corliss engine, 159- 
160. 

Lap and lead of, 134-156. 

Placing central, 154-155. 

Rotative, 158. 

Slide, 133-157. 

Setting of, 133-160. 

Stem, length of, 154-155. 

Travel of, 134-137-140-155- 
201. 

Types of, 134. 
Valve, Safety — 

Frequent testing of, 79. 

Lever, 39-40-77. 

Pop, 39. 

Ratio of area to grate sur- 
face, 39-40. 

U. S. Marine rule for, 77. 
Valves — 

For feed pump, 80. 

Water — 

Boiling point of, 105-106. 
Chemical treatment of, 104. 
Composition of, 103. 
Contraction and expansion of, 

104-105. 
Foaming, 76. 
Impurities in, 104. 
Quantity required for con- 
denser, 273-276. 
Weight of, 105. 



VTII 



Washing out Boiler; — 
Preparing for, 72. 
Proper method of, 73-74. 

Water Columns — 

Proper location of, 34-35. 
How to connect to boiler, 

35-36. 
Dangerous condition of, 37. 

Wire drawing, 191. 



Work- 
Definition of, 195. 
External, 108. 
Internal, 108. 

Wrist Plate- 
Vibration of, 162. 
Adjustment of, 163. 

Zeuner valve diagrams, 
145-148. 



139- 



PART II 

STEAM ENGINEERING 
LIST OF ILLUSTRATIONS 



American underfeed stoker, Electrically operated valve 
348. (Curtis turbine), 380. 



Branca's steam turbine, 358. 
Burke furnace, 353. 

Cahall boiler fitted with auto- 
matic stoker, 337. 

Curtis steam turbine (general 
view), 372. 

Curtis steam turbine, under 
construction, 373. 

Curtis steam turbine — station- 
ary and revolving buckets, 
374. 

Curtis steam turbine — nozzle 
diaphragm, 375. 

De Laval steam motor — gen- 
eral view, 394. 

De Laval diverging nozzle, 392. 

De Laval turbine wheel and 
nozzles, 393. 

De Laval steam turbine — work- 
ing parts, 396. 

De Laval steam turbine — plan 
view, 398. 

De Laval steam turbine— sec- 
tional view, 399. 

De Laval steam turbine — gov- 
ernor and valve, 402. 

De Laval steam turbine — cross 
section of wheel, 404. 

Diagram of nozzles and buckets 
in a Curtis steam turbine, 
376. 

Double riveted lap joint, 305. 

Double riveted butt joint, 306. 

Double crow foot stay, 318. 



Governor of Curtis steam tur- 
bine, 379. 

Hamilton-Holzwarth steam 

turbine, 385. 
Hero's steam turbine, 357. 

Jones underfeed stoker, 351. 

Mansfield chain grate stoker, 

338. 
Murphy furnace, 344. 

Playford stoker, 339. 

Quadruple riveted butt joint, 
309. 

Roney stoker, 346. 

Triple riveted butt joint, 307. 

Vanderbilt locomotive fire box, 

314. 
Vicars mechanical stoker, 341. 

Wilkinson mechanical stoker, 

342. 
Westinghouse - Parsons steam 

turbine (general view), 360. 
Westinghouse - Parsons steam 

turbine (sectional view), 362. 
Westinghouse - Parsons steam 

turbine — open for inspection, 

361. 
Westinghouse -Parsons steam 

turbine governor, 367. 



PART II 



STEAM ENGINEERING 



INDEX 



Accumulator, 372. 

Action of steam in turbine en- 
gines, 364-377-398. 

Adiabatic expansion, 392. 

Admission of steam to turbine 
engines, 370-379. 

American stoker, 347-348-349. 

Angle irons, 314. 

Of segments, 320-321. 

Of surface to be stayed, 319. 

Balancing pistons, 365. 
Barometric condenser, 408. 
Boiler — 

Care of, 327. 

Braces and stays, 311. 

Belpaire type, 313. 

Fire cracks, 331. 

How to prepare for washing 

out, 328. 
How to fire up, 331-332. 
How to connect with main 

header, 332. 
Inspection of, 330. 
Rivet material, 298. 
Stay bolts, 313. 
Steel plate — specifications 

for, 296. 
Tensile strength of plate, 

296. 
Thurston's specifications for 
rivets, 298. 

Calculating strength of stayed 

surfaces, 319. 
Channel bar, 317. 
Clearance in turbine engines, 

365-374-383. 
Clinker on furnace walls, 330. 
Coxe mechanical stoker, 338. 



Crown — 

Bars, 313. 

Bolts, 313. 

Sheet, 313. 
Crow foot brace, 311-312. 
Curtis steam turbine, 370. 

Action of steam in, 377. 

Efficiency of, 381. 

Expanding nozzles of, 371 . 

Guide bearings of, 373. 

Lubrication of, 371. 

Ratio of expansion in four 
stage machine, 371. 

Stationary blades — function 
of, 374. 

De Laval steam turbine, 392. 

Action of steam in, 397-400. 

Conversion of heat into work, 
395. 

Diverging nozzles of, 392. 

Efficiency, tests of, 404-405. 

Flexible shaft of, 400-402. 

Gear wheels of, 400. 

Governor, 402-403. 

Vacuum valve, 403. 
Diameters of rivets, 299-300. 
Dished heads, 325. 
Double riveted butt joints, 299- 

303-306. 
Double riveted lap joints, 300- 

305-306. 
Double crow foot brace, 318. 

Efficiency — 

Of double riveted lap joint, 

305-306. 
Of double riveted butt joint, 

307. 
Of triple riveted butt joint, 

307. 



Efficiency — 

Of quadruple riveted butt 

joint, 309-310 
Of Westing-house - Parsons 

steam turbine, 368. 
Of Curtis steam turbine, 380- 

381. 
Of De Laval steam turbine, 

404. 

Factor of safetv, 324. 
Flexible coupling, 366-387. 
Flexible shaft, 400. 
Floating journal, 366. 
Floating fulcrum, 367. 
Fusible plug, 329. 

Gusset stays, 314. 

Hamilton - Holzwarth steam 

turbine, 382. 
Action of steam in, 385-386. 
Development of, 382. 
Distribution of steam in, 

386. 
Device for changing speed of, 

389. 
Flexible couplings of, 387. 
Governor, 387-388. 
Lubrication of, 390. 
Regulating mechanism, 388- 

389. 
Running wheels, 384. 
Stationary disks, 383. 
Thrust ball bearing, 387. 

Inspectors, U. S. Board of, 

296-311. 
Inspection of boilers, 330. 

Jones underfeed stoker, 351- 
352. 

Kinetic energy of steam, 357- 
391-400. 

Lost work, 368. 

Man-holes for boilers, 330. 
Mechanical stokers, 334. 
Murphy furnace, 341-342-343. 



Nozzle — 

Expanding, 391-395. 
Valves, 395. 

Outside furnaces, 353-354. 

Parallel flow of steam in tur- 
bine engines, 359. 

Pitch— 

Of rivets, 299-300. 
For stays, 319. 

Playford stoker, 339. 

Punched and drilled boiler 
plates, 297. 

Quadruple riveted butt joint, 

308. 
Quintuple riveted butt joint, 

308. 

Rivets — 

Crushing resistance of, 305. 

Diameter and pitch of, 300. 

Material for, 297. 

Shearing strength of, 298. 
Riveted joints — 

Calculations for efficiencies 
of, 306-307-308-309-310. 

Double lap and butt, 302. 

Single lap, 302. 

Triple riveted butt, 303. 

Quadruple riveted butt, 309. 

Quintuple riveted butt, 309. 
Riveting machine, 302. 
Roney stoker, 345-346 

Stayed surfaces — 

Areas of, 320. 

Strength of, 319-320-323. 
Steam turbine — 

Branca's turbine, 359. 

Disposal of exhaust steam, 
406. 

Efficiency of, 381. 

Hero's turbine, 359. 

Main requisite for quiet run- 
ning, 387. 

Two- main sources of econ- 
omy, 380-411. 

Types of, 359. 



Tables- 
Diameters of rivets, 298. 

Diameters and pitch of rivets 
in double riveted joint, 
300. 

Kent's rules for thickness of 
plate and diameter and 
pitch of rivets, 301. 

Lloyd's rules for thickness of 
plate and diameter of riv- 
ets, 300. 

Proportions of single riveted 
lap joints, 302. 

Proportions of double riveted 
lap and butt joints, 303. 

Proportions of triple riveted 
butt joints, 304. 

Through stays, 314-316-317. 

Thurston's table of joint ef- 
ficiencies, 301. 

Triple riveted butt joint, 303- 
304-307. 
Turbines (steam) — 

Branca's turbine, 359. 

Disposal of exhaust steam, 
406. 

Efficiency of, 380. 

Hero's turbine, 359. 

Main requisites for quiet run- 
ning, 387. 

Types of, 359. 

Unstayed surfaces — 
» Rule for finding strength of, 
324. 



Vacuum — 

Advantages of, 407-409. 

Valve, 403. 
Vanderbilt locomotive fire box, 

313. 
Velocity — 

Force of, 380. 

Of escaping steam, 360-361. 

Work done by, 377-378. 
Vicars mechanical stoker, 340. 



Water column for boiler, 330. 
Welded seams, 325. 
Westinghouse - Parsons steam 

turbine — 

Action of steam in, 364-365. 

Clearances in, 364. 

Efficiency of, 369. 

Floating journal, 367. 

Governor, 367. 

Principles of, 359. 

Perfect balance of, 368. 

Speed of, 360. 

Stationary and moving 
blades of, 363-364. 
Wheels — 

Impulse, 360. 

Reaction, 360. 

Running, 384. 
Wilkinson stoker, 340-341 



PART III 
INDEX 



ELECTRICITY FOR ENGINEERS 



Ammeters, 137. 

alternating current, 143. 

shunt, 138. 
Ampere, definition of, 7. 

hour, definition of, 9. 

milli, definition of, 10. 

turns, definition of, 42. 
Arc Lamp, alternating current, 
168. 

brush, 155. 

constant current, 154. 

constant potential, 165. 

enclosed, 167. 

principle of, 153. 

Thomson-Houston, 160. 

Western Electric, 169. 
Armature, location of faults, 61. 

Balanced three- wire system, 

23. 
Booster, 198. 
Brush system, 77. 

controller, 84. 
Brushes, care of, 53. 

construction of, 53. 

shifting of, 62. 

setting of, 59. 

staggered, 55. 

Calculation of wires, 25. 
Center of Distribution, 25. 
Circuit breakers, 117. 
Circular mil, definition of, 26. 
Collector rings, 125. 
Coulomb, definition of, 10. 
Commutator, area allowed for 
current, 51. 

care of, 53. 

construction of, 49. 
Conductivity, definition of, 16. 
Conductors, 7. 
Constant current system, 20. 



Constant potential system, 20. 
Current, 5. 

generation of, 40. 

single phase, 129. 

two and three phase, 130. 
Cut-out box, 25. 

Distributing center, 24. 
Divided circuits, 16. 
Dvnamos, alternating current, 
122. 

brush, 77. 

care of, 64. 

compound wound, 47. 

failure to generate, 67. 

operation of constant cur- 
rent, 75. 

operation of constant poten 
tial, 65. 

operation in parallel, 69. 

reversal of current, 44. 

separate exciting, 123. 

series, connections of, 45 

shunt, connections of, 46. 

test for polarity, 70. 

Thomson-Houston, 89. 

Electromagnet, 41. 
Electromotive force, definition 

of counter, 108. 
Electroplating, 199. 
Electrolysis, 199. 
Electrolytic action, 9. 
Equalizer bar, 72. 

Feeders, 24. 
Fuses, 117. 

Gramme Ring, 44. 
Ground detectors, 185. 

Heating by electricity, 201= 
Horse power, 15. 



Incandescent lamps, 172. 

current required, 175. 

efficiency tables, 173. 
Insulators, 7. 

Joints in wires, 31. 
Joule, 15. 

Kilowatt hour, 15. 

Laminated armature, 53. 
Light, absorbtion of, 176. 
Lightning arresters, 204. 

Thomson, 206. 
Lines of force, definition of, 41. 

direction of, 42. 
Loss in wires, 27. 

Magnet, soft iron, 5. 

steel, 5. 
Meters, reading of, 147. 
Mil, circular, 26. 

square, 26. 
Motors, 107. 

alternating current, 116- 

compound, 112. 

series, 111. 

shunt, 110. 
Multiple arc system, 20 
Multiple series system, 21. 

Negative wire, 23. 
Nernst lamp, 177. 
Neutral point of dynamo, 49. 
Neutral wire, 22. 

Ohm, 13. 
Ohm's law, 14. 

Parallel system, 19. 
Photometer, Bunsen, 190. 

Rumford's, 191. 
Polarity indicator, 142. 
Positive wire, 23. 
Potential, difference of, 10. 
Prony brake, 187. 

Regulator, Brush, 85. 
series dynamo, 45. 



Resistance box. 46. 

definition of, 13. 

effect of heat on, 13. 
Rheostat for shunt dynamo, 66. 

Series arc system . 20. 

circuit, 6. 

multiple sj^stem, 20. 
Service wires, 25 
Short circuit, 11. 
Speed controller, 114. 
Square mil, 26. 
Static electricity, 12. 
Storage batteries, 193. 

connections for, 197. 
Switchboard, arc, 101. 

arc, 104. 

constant potential, 73. 

Testing lines, 181. 

dynamo efficiency, 187. 

grounds, 184. 

open circuits, 181. 

short circuits, 183. 
Thomson-Houston system, 89. 

controller, 97. 
Three-wire system, 22. 
Transformer, principle of, 130 

rotary, 128. 

Volt, definition of, 10. 
Voltameter, 9. 
Voltmeter, 10. 

alternating current, 143. 

magnetic vane, 137. 

Weston, 133. 

Watt, definition of, 14. 

hour, definition of, 15. 
Wattmeters, 144. 

Thomson, 145. 
Wires, carrying capacity of, 38. 

properties of, 39. 

weights of copper, 37. 
Wiring tables, 32. 
Wiring systems, 19. 



INTRODUCTION 



ENGINEERING DIVISION 



In the following pages the author proposes to oleal 
mainly with the operation of steam engines, boilers, 
feed pumps, and all the necessary adjuncts of a steam 
plant, rather than with the co?istmctioii and erectio?i of 
the same, although the designing and construction of 
steam machinery will receive some attention. 

In order to successfully operate a steam plant the 
engineer in charge should, in addition to his other 
accomplishments, have at least sufficient technical 
knowledge to enable him to ascertain, by measure- 
ments and calculations, such very important points as 
the safe working pressure of his boiler, the most eco- 
nomical point of cut off for his engine, whether engine 
and boiler are properly proportioned for the work to 
be performed, and many other details which will be 
treated upon in their proper place. 

Without a doubt the most successful operating 
engineers are those who combine practice with theory, 
and in order to obtain a practical working knowledge 
of steam engineering it is absolutely necessary that 
the young man who desires to become a successful 
engineer should start in the boiler-room, that he 
should thoroughly familiarize himself with' all of the 
details of boiler management, and while his hands 
and eyes are thus gradually being trained to the prac- 
tical part of the work he should at the same time be 
training his mind in the theoretical part by reading 
and studying technical books and journals relative to 
steam engineering. In order to facilitate this work a 
9 



10 . INTRODUCTION 

series of practical questions will follow the close of 
each chapter, the answers to which may be found in 
the matter contained in the chapter. And now with 
the hope that a study of the following pages may prove 
to be a help to all into whose hands this book may 
come, the author respectfully dedicates it to his fellow 
craftsmen, the engineers of America. 

C. F. S. 



Engineering 

CHAPTER I 
THE BOILER 

Description of various types — Construction — Rules for ascertain- 
ing strength of sheet before and after punching — Strength of 
rivets — Single and double riveted seams — Triple riveted butt 
joints, strength of — Force tending to rupture a boiler — Rules 
for finding the safe working pressure of boilers — gracing — 
Rules for bracing — Bracing domes. 

It is hardly within the scope of this book to describe 
the many and varied types of metallic vessels known 
as steam boilers in use to-day for the generation of 
steam for power and other purposes. The author will 
deal mainly with those types most commonly used in 
this country for stationary service. 

Description. These may be divided into four differ- 
ent classes. The first and most simple type, and the 
one from which the others have gradually evolved, is 
the plain cylinder boiler in which the heated gases 
merely pass under the boiler, coming in contact only 
with the lower half of the shell and then pass to the 
stack. These boilers are generally of small diameter 
(about 30 in.) and great length (30 ft.). Next comes 
the flue cylindrical boiler, which is somewhat larger in 
diameter than the former, generally 40 in. diameter 
and 20 to 30 ft. long, with two large flues 12 to 14 in. 
diameter extending through it. The return tubular 
boiler, consisting of a shell with tubes of small diam- 
11 



12 



ENGINEERING 



eter (2 to 4 in.) extending from head to head through 
which the hot gases from the furnace pass on their 
way to the stack. This boiler, which comes in the 
third class, is probably more extensively used in the 
United States for stationary service than any other 
type. The fourth class comprises the water tube boil- 
ers, in which the water is carried in tubes 3 to 4 in. in 
diameter, sometimes vertical and sometimes inclined, 
and connected at the top to one end of a steam drum, 




STANDARD HORIZONTAL BOILER WITH FULL-ARCH FRONT SETTING. 



and having the lower ends of the tubes connected to a 
mud drum, which is also connected to the opposite end 
of the steam drum, thus providing for a free circula- 
tion of the water. Of the latter type there have been 
many different kinds evolved during the last one hun- 
dred years, the majority of them having had but a 
brief existence, being compelled to obey the inex- 
orable law of the survival of the fittest, and to-day 
there are a few excellent types of water tube boilers 



THE BOILER 



IS 



which have become standard and are being extensively 
used. The margin of safety as regards disastrous 




WICKES VERTICAL WATER TUBE BOILER, 

explosions appears to be in favor of the water tube 
boiler. It is not contended that they are entirely 



14 



ENGINEERING 



exempt from the danger of explosion. On the con- 
trary, the percentage of explosions of water tube boil- 
ers in proportion to the number in use is probably as 
large, if not larger, than it is with boilers of the shell 
or return tubular type, but the results are seldom so 
destructive of life or property, for the reason that if 
one or more of the tubes give way the pressure is 
released and the danger is past. 




500 HORSE POWER HEINE WATER TUBE BOILER. 



Construction. As the four classes of boilers above 
referred to are constructed of similar material, although 
assembled in different ways, the standard rules for 
calculating strength of joints, bracing, etc., may be 
applied to all. 

The shell should be made of homogeneous steel of 
about 60,000 lbs. tensile strength. The thickness 
depending upon the pressure to be carried. The term 



THE BOILER 15 

tensile strength means that it would take a pull of 
60,000 lbs. in the direction of its length to break a bar 
of the material one inch square, or two inches wide by 
one-half inch thick, or three-eighths of an inch thick 
by 2.67 in. wide. 

The heads are generally made one-eighth of an inch 
thicker than the shell. 

Riveting. Boiler rivets should be of good charcoal 
iron, or a soft, mild steel of 38,000 lbs. to 40,000 lbs. 
T. S. No boiler is stronger than its weakest part, and 
it is evident that a riveted joint has not the full 
strength of the solid plate. In order to ascertain the 
safe working pressure of a boiler it is necessary to first 
determine the strength of the riveted seams, and the 
method of doing this is as follows: Assume the boiler 
to be of the horizontal tubular type, 60 in. in diameter 
by 16 ft. in length. The plates to be of steel ^ in. 
thick, having a tensile strength of 60,000 lbs. per 
square inch, the longitudinal seams to be double 
riveted and the girth seams to be single riveted. The 
pitch of the rivets, that is the distance from the center 
of one rivet hole to the center of the next one in the 
same row, to be for the double riveted seams 3^ in. 
and for the single riveted seams 2}i in. The diameter 
of the rivets to be yk in. and diameter of holes to be 
\\ in. Assume the rivets to have a T. S. of 38,000 lbs. 
per square inch of sectional area. First, find strength 
of a section of solid plate 3^ in. wide, which is the 
width between centers of rivet holes before punch- 
ing. 

Rule 1. Pitch x thickness x T. S. Thus, 3.25 x .375 x 
60,000 = 73,125 lbs., strength of solid plate. 

Second, find strength of net section of plate, mean- 
ing that portion of plate left after deducting the diam- 



16 



ENGINEERING 



eter of one hole || in., which expressed in decimals 
= .9375 in. from the width of plate before punching. 

Rule 2. Pitch - diameter of hole x thickness x T. S. 
Thus, 3.25 - .9375 x .375 x 60,000 = 52,031 lbs., strength 
of net section of plate. 

Third, find strength of rivets. In calculating the 
strength of rivets in a double riveted seam, the sec- 
tional area of two rivets must be considered, taking 




BABCOCK AND WILCOX BOILER. 



one-half the area of two rivets in the first row, and the 
area of another rivet in the second row. The area of 
a %-in. rivet is .6013 in., but when in position it is 
assumed to fill the hole \\ in. Consequently, its area 
would then be .69 in. and its strength is found by 
Rule 3. 

Rule j. Sectional area x T. S. Thus, .69x38,000 = 
26,220 lbs. , strength of one rivet, and multiplying by 2, 
as there are two rivets, the result is 26,220 x 2 = 52,440 



THE BOILER 



17 



Jbs., strength of. rivets in the seam under considera- 
tion. It thus appears that the plate is the weakest por- 




VERTICAL FIRE BOX BOILER. 



tion and the percentage of strength retained is found 
by multiplying $2,031 by 100 and dividing by 73,12$, 



18 ENGINEERING 

the strength of solid plate. Thus, =71.1 

per cent. 

The query might arise, why is the diameter of one 
rivet hole deducted from the pitch when figuring the 
strength of net plate? The answer is, that in punching 
the holes one-half the diameter of each hole is cut 
from the section designated, thereby reducing its width 
by just that amount. 

The 71. 1 per cent, obtained by the calculation rep- 
resents the strength of the boiler as compared to the 
strength of the sheet before punching, and should enter 
into all calculations for the safe working pressure. 

It is usual in practice to figure the strength of a 
double-riveted seam at yo per cent, of the strength of 
the solid plate. The strength of triple-riveted butt 
joints may be calculated by taking a section of plate 
along the first row of rivets and estimate it as a single- 
riveted joint, then add to this result the strength of 
rivets in the second and third rows for a section of the 
same width. In properly designed triple-riveted butt 
joints the percentage of strength retained is 88, and 
some recent achievements in designing have shown the 
remarkable result of quadruple-riveted butt joints 
retaining as high as 92 to 94 per cent, of the strength 
of the solid plate. 

Bursti?ig Pressure. The query might arise, why 
should the longitudinal or side seams require to be 
stronger than the girth or round about seams? The 
answer is, that the force tending to rupture the boiler 
along the line of the longitudinal seams is proportional 
to the diameter divided by two, while the stress tend- 
ing to pull it apart endwise is only one-half that, or 
proportional to the diameter divided by four. 



THE BOILER 19 

To illustrate, let Fig. i represent the shell of the 
boiler heretofore referred to, ignoring for the time 
being the tubes and braces, and consider the boiler 
simply as a hollow cylinder. Now the total force 
tending to rupture the boiler along the line of the girth 
seams or in the direction of the horizontal arrows = area 
of one head in square inches x pressure in pounds per 
square inch. It is true that the pressure is exerted 
against both heads, but the area of one head can- only 
be considered for the reason that the two stresses are 
exerted against each other just as in the case of two 
horses pulling against each other, or in opposite direc- 
tion on the same chain. The stress on the chain will 



g A B 



be what each horse (not both) pulls. To further illus- 
trate, suppose one of the horses to be replaced by a 
permanent post or wall and let one end of the chain be 
attached thereto. One head or one side of the boiler 
pulls against the other, and the stress on the seams is 
the force with which each (not both) pulls. Referring 
again to Fig. I, area of one head = 6cr x .7854 = 2827.4 
sq. in. Suppose there is a pressure of 10 lbs. pet- 
square inch in the boiler. Then total stress on the 
girth seams = 2827.4 x 10 = 28,274 lbs. Opposed to this 
pull is the entire circumference of the boiler, which is 
60 x 3.1416= 188.5 m - Therefore, dividing total pres- 
sure (28,274 lbs.) by the circumference in inches (188. 5) 
will give 150 lbs. as the stress on each inch of the 



c 20 • ENGINEERING 

girth seams. While the stress on each inch of the 
longitudinal seams or along the line A B, Fig. i, and 
which is exerted in the direction of the vertical arrows, 
is pressure (10 lbs.) x one-half the diameter (30 in.) 
= 300 lbs. One-half the diameter is used because the 
pressure in any direction is effective only on the sur- 
face at right angles to that direction. 

The formula for finding the bursting pressure of a 
boiler may be expressed as follows: 

T S x T . 
B = ' in which B = bursting pressure. 

T.S. = tensile strength. 
T= thickness of sheet. 
R= radius or one-half the cliam. , 
Example. T. S. = 55,000 lbs. per square inch. 

T = ys in. (expressed decimally = .375 

in.). 
R = 30 in. 
Then 55,000 x .375 -f- 30 = 687.5 l° s - P er square inch, 
which is the pressure at which rupture would take 
place provided there were no seams in the boiler and 
the original strength of the sheet was retained, but, as 
has been seen, a certain percentage of strength is lost 
through punching or drilling the necessary rivet holes, 
and this must be taken into account. 

The formula now becomes, for double riveting, 

B =— — '- — = — , in which the letters preserve the same 

value as in the original formula, but the result is 
reduced by multiplying by the decimal .70, which rep- 
resents the percentage of strength retained by double- 
riveted seams. Consequently B will now = 

55.ooox.375x.70 8llbs . 
30 
In case the seams are all single riveted .56 must be 



THE BOILER 21 

substituted for .70, and with triple-riveted butt joints 
.88 can safely be used. 

Safe Working Pressure. In order to ascertain the safe 
working pressure of a boiler it is necessary first to cal- 
culate the bursting pressure and divide this by another 
factor called the factor of safety. The one most com- 
monly used for boilers is 5, or in other words the safe 
working pressure = one-fifth the bursting pressure. In 
the case of the boiler under consideration, the safe 
pressure would be 481 ■*- 5 = 96 lbs., at which point the 
safety valve should blow off. 

Bracing. Every engineer can easily ascertain for 
himself whether the boilers under his charge are 
properly braced or not. The parts that require bra- 
cing are: all flat surfaces, such as the sides and top of 
the fire-box in boilers of the locomotive type, and 
those portions of the heads above and below the tubes 
in horizontal tubular boilers, also the top of the dome. 

The stress per square inch of sectional area on braces 
and stays should not exceed 6,000 lbs. It is custom- 
ary to consider the flange of the head and the top row 
of tubes as sufficient bracing for a space two inches 
wide above the tubes and the same distance aruund the 
flange. Therefore the part of the head to be braced 
will be the segment contained within a line drawn two 
inches above the top row of tubes and two inches inside 
the flange. 

In order to ascertain the number of braces required 
for a given boiler he^ad, three factors are necessary: 
first, the area of the segment in square inches; second, 
the diameter and T. S. of the braces, and third, the 
pressure to be carried. By the use of Table No. 1 the 
areas of segments of boiler heads ranging from 42 to 72 
in. in diameter can easily be obtained. Assume the 



ENGINEERING 



boiler to be 60 in. in diameter, distance from top of 
tubes to top of shell 24 in. Deduct 4 in. for surface 
braced by top row of tubes and flange, leaving the 
height of segment to be braced 20 in. 



TABLE I 



Diameter 
of Boiler. 


Ditsance from 
Tubes to Shell. 


Height of 
Segment. 


Constant. 


42 in. 


15 in. 


11 in. 


.16314 


44 in. 


17 ni. 


13 in. 


.1936 


48 in. 


19 m. 


15 m. 


.20923 


54 m. 


21 m. 


17 in. 


.21201 


60 in. 


24 in. 


20 in. 


.22886 


66 in. 


25 m. 


21 in. 


.214 


72 in. 


29 in. 


25 in. 


.24212 



Rule. Multiply the square of the diameter of the 
boiler by the constant number found in right hand col- 
umn opposite column headed diameter. 

Example. 60 x 60 x .22886 = 823.89 sq. in., area of 
segment to be braced. Find number of braces 
required. Assume the braces to be ij4 in. in diam- 
eter and of a T. S. of 38,000 lbs. per square inch of 
section. The area of one brace will be .994 sq. in., 
which x 6,000 lbs. gives 5,964 lbs. as the stress allow- 
able on each brace. Suppose the pressure to be car- 
ried is 100 lbs. per square inch. There will be area of 
segment (823.89 sq. in.) x pressure (100 lbs.) = 82,389 
lbs., total stress. Dividing this result by 5,964 lbs. 
(the capacity of each brace) gives 13.8 braces as the 
number needed. In practice there should be fourteen. 

Having a T. S. of 38,000 lbs. and using 6 as the 
factor of safety, each brace could safely sustain a pull 
of 6,295 lbs. Therefore it is evident that the above 
mentioned load for each brace is well within the limit. 
For convenience in calculating the areas of segments 



THE BOILER 




of circles, other than those mentioned in Table I, the 
following rule is given: 

Referring to Figure 2 it is desired to find the area of 
t/-'e segment contained within the lines A B C E. It 
will be necessary first to find the area of the sector 
bounded by the lines A B C D. This is done by mul- 
tiplying one-half the length of 
the arc, A B C, by the radius, 
D B. Having obtained the 
area of the sector, the next / 
step is to find the area of the 
triangle bounded by the lines 
A E.C D and subtract it from 
the area of the sector. The 
remainder will be the area of 
the segment. Having found 

the area of the surface to be braced, and the number 
of braces required, it now becomes necessary to con- 
sider the spacing of the same. 

Rule. Divide area to be braced by the number of 
braces, and extract the square root of quotient. 

Example. 823.89- 14= 58.8 sq. in. to be allotted to 
each brace. Extract square root of 58.8 and the 
result is 7.68 inches, which is the length of one side of 
the square which each brace will be required to sus- 
tain. 

For internally fired boilers the same rules can be 
applied except that the surfaces to be braced are 
generally of rectangular shape and consequently the 
area is more easily figured than in the case of seg- 
ments. That part of the head below the tubes also 
requires to be braced, and two braces are generally 
sufficient, as at A and B, Fig. 3. In the case of domes 
it is safe to consider the portion of the head within 



24 



ENGINEERING 



three inches of the flange as sufficiently braced. Then 
suppose the dome to be 36 in. in diameter, there will 
remain a circle 30 in. in diameter to be braced. The 
circumference of this circle is 94.2 in. and the pitch, 
or distance from center to center of the braces, being 

7.6 in., the number of 
braces required is 
found by dividing 94.2 
b y 7-6, giving 12 
braces. These braces 
should be located 
along a line which is 
one-half the pitch, or 
3.8 in., within the cir- 
cumference of the 30- 
in. circle. The space 
immediately surround- 
ing the hole cut for 
the steam outlet will 
be sufficiently reen- 
forced by the flange riveted on for the reception of the 
steam pipe. All holes cut in boilers, such as man 
holes, hand holes, and those for pipe connections, 
above two. inches should be properly reenforced by 
riveting either inside or outside a wrought-iron or steel 
ring or flange of such thickness and width as to con- 
tain at least as much material as has been cut from 
the hole. 

Questions 

1. How many types of steam boilers are there? 

2. What kind of boilers are included in type one? 

3. Describe a boiler belonging to type two. 

4. Describe a boiler of the third type. 




figure 3. 



THE BOILER 25 

5. How is a boiler of the fourth type constructed? 

6. In what respect do water tube boilers have the 
advantage over other types as regards explosions? 

7. What kind of material should be used in the con- 
struction of boilers? 

8. What does the term tensile strength (T. S.) 
mean? 

9. What is the usual T. S. of steel boiler plates? 

10. How much thicker than the shell plates should 
the heads be? 

11. Of what material and of what T. S. should the 
rivets be? 

12 Is a riveted joint as strong as the solid plate? 

13. What is meant by the pitch of the rivets? 

14. What is the usual pitch for a double riveted 
seam? 

15. Give the rule for finding the strength of the solid 
plate before punching. 

16. What is meant by net section of plate? 

17. What is the rule for finding strength of net sec- 
tion of plate? 

18. How is the strength of rivets in a double riveted 
seam calculated? 

19. What percentage of the strength of solid plate is 
usually retained in a double riveted seam? 

20. How is the strength of a triple riveted butt strap 
joint calculated? 

21. What per cent, of the original strength of the 
sheet is retained in a properly designed triple riveted 
butt strap joint? 

22. Why should the side seams be stronger than the 
girth seams? 

23. What is the rule for finding the bursting pressure 
of a boiler? 



26 ENGINEERING 

24. How is the safe working pressure of a boiler 
calculated? 

25. What parts of a boiler require bracing internally? 

26. What stress per square inch of sectional area 
may be allowed on braces? 

27. How is the number of braces required for any 
part of the boiler obtained? 

28. How should domes.be braced? 



CHAPTER II 
BOILER SETTINGS AND APPURTENANCES 

Foundations — Brick work, etc. — Grate surface — Insulation — Water 
columns — Steam -gages— Safety valves — Rules for finding 
areas of — Fusible plugs and where to place them — Domes and 
mud drums — Feed pipes — A good arch for the back connec- 
tion — Blow off pipes and cocks — Surface blow off and circulat- 
ing system — Feed pumps and feed water heaters— Injectors — 
Saving effected by heating the feed water with exhaust 
steam — Apparatus for making coal tests— Heating surface — 
Rules for figuring the same. 

Settings. In the case of internally fired boilers the 
matter of setting resolves itself into the simple point 
of securing a sufficiently solid foundation, either of 
stone or brick laid in cement, for the boiler to rest 
upon. 

But with horizontal tubular or water tube boilers the 
matter of brick work becomes important, and partic- 
ular attention should be paid to securing a good foun- 
dation for the walls and great care exercised in building 
them in such manner that the expansion of the inner 
wall or lining will not seriously affect the outer walls. 
This can be done be leaving an air space of two inches 
in the rear and side walls, beginning at or near the 
level of the grate-bars and extending as high as the 
fire line, or about the center line of the boiler. Above 
this height the wall should be solid. Fig. 4 shows a 
plan and an end elevation illustrating this idea. The 
ends of some of the bricks should be allowed to project 
at intervals from the outer walls across the air space, 
so as to come in touch with the inner walls. 
27 



28 



ENGINEERING 



Where boilers are set in batteries of two or more the 
middle or party walls should be built up solid from 
the foundation. All parts of the walls with which the 




FIGURE 4. 

fire comes in contact should be lined with fire brick, 
every fifth course being a header to tie the lining to 
the main wall. 

Bridge walls should be built straight across from 
wall to wall of the setting, and should not be curved to 
conform to the circle of the boiler shell. The proper 



-4 




FIGURE 5. 

distance from the top of the bridge wall to the bottom 
of the boiler varies from eight to ten inches, depend- 
ing upon the size of the boiler. The space back of the 



BOILER SETTINGS AND APPURTENANCES 



29 



bridge wall, called the combustion chamber, can be 
filled in with earth or sand, and should slope gradually 
downward from the back of the bridge wall to the floor 
level at the rear wall, and should be paved with hard 
burned brick. The ashes and soot can then be easily 
cleaned out by means of a long-handled hoe or scraper 
inserted through the cleaning out door, which should 
always be placed in the back wall of every boiler set- 
ting. 

Back Arches. A good and durable arch can be made 




FIGURE 6. 



for the back connection, extending from the back wall 
to the boiler head, by taking flat bars of iron S/ 8 x 4 in., 
cutting them to the proper length and bending them 
in the shape of an arch, turning four inches of each 
end back at right angles, as shown in Fig. 5-. The 
distance O-B should equal that from the rear wall to 
the boiler head, and the height, O-A, should be about 
equal to O-B, and should bring the point A about two 
inches above the top row of tubes. The clamp thus 
formed is filled with a course of side arch fire brick, 



30 



ENGINEERING 



Fig. 6, and will form a complete and self-sustaining 
arch, the bottom, B, resting on the back wall, and the 
top, A, supported by an angle iron riveted across the 
boiler head about three inches above the top row of 
tubes. See Figs. 7 and 8. 

Enough of these arches should be made so that when 
laid side by side they will cover the distance from one 
side wall to the other across the rear end of the boiler. 
A fifty-four-inch boiler would thus require, six clamps, 




FIGURE 7. 



a sixty-inch boiler seven clamps, and a seventy-two- 
inch boiler would require eight clamps; the length of 
a fire b*rick being about nine inches. In case of needed 
repairs to the back end of the boiler the sections can 
be lifted off, thus giving free access to all parts, and 
when the repairs are completed the arches can be reset 
with very little trouble and much less expense than the 
building of a solid arch would necessitate. This form 
of segmental arch allows ample freedom for expansion 



BOILER SETTINGS AND APPURTENANCES 



31 



of the boiler, in the direction of its length, without 
leaving an opening when the boiler contracts. 

The crosswise construction of arch bars, while afford- 
ing equal facility in repair work, is necessarily more 
expensive than the form here described, and is also 
open to the objection that it cannot follow the con- 
tracting boiler and maintain a tight joint or connection 




FIGURE 8. 



between the back arch and the rear head above the 
tubes. 

Boiler walls should always be well secured in both 
directions by tie rods extending throughout the entire 
length and breadth of the setting, whether there be one 
boiler or a battery of several. The bottom rods 
should be laid in place at the floor level when starting 
the brick work, and the top rods extending transversely 
across the boilers can be laid on top of the boilers. 



32 ENGINEERING 

The top rods extending from front to back can be laid 
in the side walls or rest on top of them. All tie rods 
should be at least one inch in diameter, and for batter- 
ies of several boilers they should be larger. The rods 
should extend three or four inches beyond the brick 
work, with good threads and nuts on each end to 
receive the buck stays. In laying down the transverse 
tie rods they should be located so as to allow the buck 
stays to bind the brick work where the greatest con- 
centration of heat occurs. 

Horizontal boilers should always be set at least one 
inch lower at the back end than at the front, to make 
sure that the rear ends of the tubes will be covered 
with water so long as any appears in the gauge glass, 
provided of course that the lower end of the glass is 
properly located with reference to the top row of 
tubes, which will be discussed later on. Upon the 
brick work and immediately under each lug of the 
boiler there should be laid in mortar a wrought or cast 
iron plate several inches larger in dimension than the 
bearing surface of the lug and not less than one inch in 
thickness. Upon each of these plates there should be 
placed two rollers made of round iron ion^ in. in 
diameter, and as long as the width of the lug. These 
rollers should be placed at right angles to the length 
of the boiler, in such a position that the lug will bear 
equally upon them. The object of the rollers is to 
prevent disturbance of the brick work by the endwise 
expansion and contraction of the boiler. 

Grate Surface. The number of square feet of grate 
surface required depends upon the size of the boiler. 
A good rule and one easy to remember is to make the 
length of the grates equal to the diameter of the boiler. 
The width, of course, will depend upon the construe- 



BOILER SETTINGS AND APPURTENANCES 33 

tion of the furnace. If the fire brick lining is built 
perpendicular, the width of grate will be about equal 
to the diameter of the boiler. On the other hand, if 
the lining is given a batter of three inches, starting at 
the level of the grate, then the width will be reduced 
six inches. It is customary to allow one square foot 
of grate surface to every 36 sq. ft. of heating surface. 
The distance of the grate-bars from the shell of the 
boiler varies from 24 to 28 in., according to the dimen- 
sions of the boiler. 

Insulation. All boilers should be well protected 
from the cooling influence of outside air, if economy 




M CLAVE' S GRATES. 

of fuel is any object. The tops of horizontal boilers 
should be covered with some kind of heat insulating 
material, or arched over with common brick, leaving a 
space of two inches between the boiler and the arch. 
The resulting saving in fuel will far more than com- 
pensate for the extra expense in a very short time. 
All cracks in the side and rear walls should be care- 
fully pointed up with mortar or fire clay. One source 
of heat loss in return flue boilers is short circuiting 
from the furnace to the breeching, caused by the 
arches over the fire doors becoming loose and shaky, 
and allowing considerable of the heat to escape directly 
to the stack instead of passing under the boiler and 



34 ENGINEERING 

through the tubes. Another bad air leak often occurs 
at the back connection when the arch rests wholly 
upon iron bars imbedded in the side walls. This leak, 
as has already been noted, is caused by the expansion 
of the boiler, which gradually pushes the arch away 
from the back head until, in the course of time, there 
will be a space of $/% in. and sometimes y± in. between 
the head and the arch. The obvious remedy for this 
is an arch that will go and come with the movement 
of the boiler, and such an arch can be secured by build- 
ing it in sections, as illustrated by Fig. 3, and then 
riveting a piece of angle iron to the boiler head, above 




m' clave' s grates. 

the top row of tubes for the upper ends of the sections 
to rest upon, as already described. It will be seen 
that within all possible range of boiler movement in 
either direction the arch will, with this construction, 
always remain close to the head. 

Water Columns. Water columns should be so located 
as to bring the lower end of the gauge glass exactly on 
a level with the top of the upper row of tubes, thus 
always affording a perfect guide as to the depth of 
water over the tubes. Many gauge glasses are placed 
too low, and water tenders and firemen are- often 
deceived by them unless their positions with relation to 
the tubes are carefully noted. 



BOILER SETTINGS AND APPURTENANCES 35 

The only safe plan for an engineer to pursue in 
taking charge of a steam plant is to seize the first 
opportunity for noting this relation. When he has 
washed out his boilers he may leave the top man-hole 
plates out while refilling them, and when the water 
stands at about four inches over the top row of tubes, 
the depth of water in the glass should be measured. 
He should do this with every boiler in the plant, and 
make a memorandum for each boiler. He will then 
know his bearings with regard to the safe height of 
water to be carried in the several gauge glasses. If he 
finds any of them are too low, he should lose no time 




m' clave' s grates, 

in having them altered to comform to the requirements 
of safety. The position of the lower gauge cock 
should be three inches above the top row of tubes. 

In making connections for the water column plugged 
crosses should always be used in place of ells. Brass 
plugs are to be preferred if they can be obtained; but 
whether of brass or iron, they should always be well 
coated with a paste made of graphite and cylinder oil 
before they are screwed in. They can then be easily re- 
moved when washing out the boiler, so as to allow the 
scale, which is sure to form in the lower connection, to 
be cleaned out. The best point at which to connect the 
lower pipe with the boiler is in the lower part of the 



36 ENGINEERING 

head just below the bottom row of tubes, and near the 
side of the boiler on which the water column is to 
stand; \% or \y 2 in. pipe should be used in all cases. 
The top connection can be made either in the head 
near the top, or in the shell. A 24 or I in. drain pipe 
should be led into the ash pit, fitted with a good reli- 




AUXILIAEY SPRING PRESSURE GAUGE. 

able valve which should be opened at frequent intervals 
to allow the mud and dirt to blow out of the water col- 
umn and its connections. This is a very important 
point, and great care should be taken to keep the 
water column and all its connections thoroughly clean 
at all times. 

One of the best indications that some portion of the 



BOILER SETTINGS AND APPURTENANCES 37 

connections between the water glass and the boiler is 
choked or plugged with scale, is when there is no per- 
ceptible movement of the water in the glass. When 
the connections are free and the boiler is being fired, 



AUXILIARY SPRING PRESSURE GAUGE, SECTIONAL VIEW. 

there is always a slight movement of the water up and 
down in the glass, and when there is no perceptible 
movement it is time to look for the cause at once. 
Many instances of burned tubes have occurred, and 



38 



ENGINEERING 



even explosions caused by low water in boilers while 
the gauge glass showed the water to be at a safe 
height. But owing to the connections having become 
plugged with scale, the water in the glass had no con- 
nection whatever with that in the boiler, and the water 
column was therefore worse than useless. 




Steam Gauges. As water columns are made at pres- 
ent the steam gauge is usually connected at the top of. 
the column. This makes a handsome and convenient 
connection, although theoretically the proper method 
would be to connect the steam gauge directly with the 
dome or the steam space of the shell. There should 
always be a trap or siphon in the gauge pipe in order 



BOILER SETTINGS AND APPURTENANCES 39 

to retain the water of condensation, so as to prevent 
the hot steam from coming in contact with the spring. 

If at any time the water is drained from the siphon, 
care should be exercised in turning on the steam 
again by allowing it to flow in very slowly at first until 
the siphon is again filled with water. 

The steam gauge and the safety valve should be com- 
pared frequently by raising the steam pressure high 
enough to cause the valve to open at the point for 
which it is set to blow. 

Safety Valves. The modern pop valve is generally 
reliable, but, like everything else, if it is allowed to 
stand idle too long it is likely to become rusty and 
stick. Therefore it should be allowed to blow off at 
least once or twice a week in order to keep it in good 
condition. 

Most pop valves for stationary boilers are provided 
with a short lever, and if at any time the valve does 
not pop when the steam gauge shows the pressure to 
be high enough, it can generally be started by a light 
blow on the lever with a hammer. 

The ratio of safety valve area to that of grate surface 
is, for the old style lever and weight valve, I sq. in. of 
valve area for each 2 sq. ft. of grate surface, and 
for pop valves I sq. in. of valve area for each 3 sq. ft. 
of grate surface. 

Each boiler in a battery should have its own safety 
valve, and, in fact, be entirely independent of its mates 
as regards safety appliances. 

One example of safety valve computation will be 
given. Suppose the grate surface of a boiler is 
5 x 6 = 30 sq. ft, what should be the diameter of the 
lever safety valve? The required area of the valve is 
30-2= 15 sq. in. Then 15^.7854=19, which is the 



40 ENGINEERING 

square of the diameter of the valve. Extracting the 
square root of 19 gives 4.35 in. diameter of valve. In 
actual practice one 5 in. or two 3 in. lever safety 
valves would be required. If a pop valve is to be used 
the required area is 30 ■*■ 3 = 10 sq. in. Then 10 - .7854 = 
12.73 = square of diameter of valve. Extract the 



POP VALVE. 



square root of 12.73 and the result is 3.6 in, = diam- 
eter of valve. In practice a 4 in. valve would be 
required. 

Fusible Plugs. A fusible plug should be inserted in 
that part of the heating surface of a boiler which is 
first liable to be overheated from lack of water. 



BOILER SETTINGS AND APPURTENANCES 



41 



In a horizontal tubular or return flue boiler the 
proper location for the fusible plug is in the back head 




INSIDE VIEW OF A POP SAFETY VALVE. 



about ij^ or 2 in. above the top row of tubes. In fire- 
box Doilers the plug can be put into the crown sheet 



42 ENGINEERING 

directly over the fire. These plugs should be made of 
brass with hexagon heads and standard pipe threads, 
in sizes y 2 , ^, I in., or even larger if desired. A hole 
drilled axially through the center and counter sunk in 
the end that enters the boiler is filled with an alloy of 
such composition that it will melt and run out at the 
temperature of the dry steam at the pressure carried 
in the boiler. Thus, if the water should get below the 
plug the dry steam, coming in contact with the fusible 
alloy, melts it and, escaping through the hole in the 
plug, gives the alarm, and in case of fire-box or inter- 
nally fired boilers the steam will generally extinguish 
the fire also. The hole is counter sunk on the inner 
end of the plug so as to retain the fusible metal against 
the boiler pressure. These plugs should be looked 
after each time the boilers are washed out, and all dirt 
and scale should be cleaned off in order that the fusible 
metal may be exposed to the heat. 

Another type of fusible plug consists of a small brass 
cylinder into one end of which is screwed a plug filled 
with a metal which will fuse at the temperature of dry 
steam at the pressure which is to be carried in the 
boiler. The other end of the cylinder is reduced and 
fitted with a small stop valve and threaded to screw 
into a brass bushing inserted into the top of the boiler 
shell. This bushing also receives at its lower end a 
piece of ^ or 3^ in. pipe which extends downwards to 
within 2 in. of the top row of tubes, or the crown sheet 
if the boiler is internally fired. The principle of the 
device is that in case the water falls below the lower 
end of the pipe, steam will enter, fuse the metal in the 
plug, and be free to blow and give warning of danger. 
Some of these appliances are fitted with whistles 
which are sounded in case the steam gets access to 



BOILER SETTINGS AND APPURTENANCES 43 

them. But even with such devices no engineer can 
afford to relax his own vigilance and depend entirely 
upon the safety appliances to prevent accidents from 
low water. 

Domes and Mud-Drums. As a general proposition, 
both mud drums and domes are useless appendages to 
steam boilers. There are, no doubt, instances where 
they may serve a purpose, but as a rule their use is of 
no advantage to a boiler. Neither are the so-called 
circulating systems, sometimes attached to return 
tubular boilers, of any real value. These consist of 
one or more 4 to 6 in. pipes extending under the boiler 
from front to back through the furnace and the com- 
bustion chamber and connected to each end of the 
boiler. 

Feed Pipes. Authorities differ in regard to the 
proper location of the inlet for the feed pipe, but 
upon one point all are agreed, namely, that the feed 
water, which is always at a lower temperature than the 
water in the boiler, should not be allowed to come 
directly in contact with the hot boiler sheets until its 
temperature has been raised to within a few degrees of 
the temperature of the water in the boiler. Cer- 
tainly one of the most fruitful sources of leaks in the 
seams and around the rivets is the practice of intro- 
ducing the feed water into the bottom either at the 
back or front ends of boilers, as is too often the case. 
The cool water coming directly in contact with the hot 
sheets causes alternate contraction and expansion, and 
results in leaks, and very often in small cracks in the 
sheet, the cracks extending radially from the rivet 
holes. It would appear that the proper method is to 
connect the feed pipe either into the front head just 
above the tubes, or into the top of the shell. The 



44 ENGINEERING 

nipple entering the boiler should have a long thread 
cut on the end which screws into the sheet, and to this 
end inside the boiler there should be connected another 
pipe which shall extend horizontally at least two- 
thirds of the length of the boiler, resting on top of the 
tubes, and then discharge. Or, what is still better, 
allow the internal pipe to extend from the entering 
nipple at the front end to within a few inches of the 
back head, then at right angles across the top of the 
tubes to the other side, and from there discharge 
downward. By this method the feed water is heated 
to nearly, if not quite, the temperature of the water in 
the boiler before it is discharged. One of the objec- 
tions to this system is the liability of the pipe inside 
the boiler to become filled with scale and finally 
plugged entirely. In such cases the only remedy is to 
replace it with new pipe. But the great advantage of 
having the water thoroughly heated before being dis- 
charged into the boiler will much more than compen- 
sate for the extra expense of piping, and the general 
idea of introducing the feed water at the top instead of 
at the bottom of the boiler is therefore recommended 
as being the best. 

The diameter of feed pipes ranges from I in. for 
small sized boilers, up to 1% and 2 in. for boilers of 54 
to 72 in. in diameter. It is not good policy to have 
the feed pipe larger than necessary for the capacity of 
the boiler; because it then acts as a sort of cooling 
reservoir for the feed water, and may cause considerable 
loss of heat. 

For batteries of two or more boilers it is necessary to 
run a main feed header, with branch pipes leading to 
each boiler. The header should be large enough to 
supply all the boilers at the same time, should it ever 



BOILER SETTINGS AND APPURTENANCES 45 

become necessary to do so. The header can be run 
along the front of the boilers just above the fire doors 
with the branch pipes running up on either side, clear 
of the flue doors and entering the front connection, or 
smoke arch, and the boiler head at a point two inches 
above the tubes. There should always be a valve in 
each branch pipe between the check valve and the 
header for the purpose of regulating the supply of 
water to each boiler, and also for shutting off the 
pump pressure in case of needed repairs to the check 
valve. Another valve should be placed between the 
check valve and the boiler. By this arrangement it is 
always possible to get at the check valve when it is 
out of order. 

Blow off Pipes. Blow off pipes should always be 
connected with the lowest part of the water space of a 
boiler. If there is a mud-drum, then of course the 
blow off should be connected with it; but if there is no 
mud-drum, the blow off should connect with the bot- 
tom of the shell, near the back head, extend down- 
wards to the floor of the combustion chamber, and 
thence horizontally out through the back wall, where 
the blow off cock can be located. 

The best blow off cocks are the asbestos packed 
iron-body plug cocks, which are durable and safe. 
A globe valve should never be used in a blow off pipe, 
because the scale and dirt will lodge in it and prevent 
its being closed tightly. A straight way or gate valve 
is not so bad, but an asbestos packed plug cock is 
undoubtedly the best and safest. 

In order to protect the blow off pipe from the 
intense heat, a shield consisting of a piece of larger 
pipe can be slipped over the vertical part before it is 
connected. 



46 



ENGINEERING 



Blow off cocks should be opened for a few seconds 
once or twice a day, to allow the scale and mud to be 
blown out. If neglected too long they are liable to 
become filled with scale and burn out. A plan which 
is said to give good results is to connect a tee in the 
horizontal part of the pipe, and from this tee run a I in. 




FIGURE 9. 

pipe to a point in the back head at the water level. 
It is claimed that this will cause a circulation of water 
in the pipe and prevent the formation of scale. 

A surface blow off is a great advantage, especially 
if the water is muddy or liable to foam. By having 
the suiface blow off connected on a level with the 



BOILER SETTINGS AND APPURTENANCES 47 

water line a large amount of mud and other matter 
which is kept on the surface by the constant ebullition 
can. be blown out. 

A combination surface blow off, bottom blow off, 
and circulating system can be arranged by a connec- 
tion such as illustrated in Fig. 9. By closing cock A 
and opening cocks B and C the bottom blow off is put 
in operation; by closing B and opening A and C the sur- 
face blow off is started, and by closing C and leaving 
A and B open the device will act as a circulating sys- 
tem. The pipe should be of the same size throughout. 
Blow off pipes should be of ample size, never less than 
i}£ in-. an d from that to 2^ in., depending upon the 
size of the boiler. 

Feed Pumps and Injectors. The belt driven power 
pump is the most economical boiler feeder, but is not 




DIFFERENTIAL VALVE, DAVIS PUMP. 

the most convenient nor the safest. When the engine 
stops, the pump stops also, and sometimes it happens 
that the belt gives way and the pump stops at iust 



48 



ENGINEERING 



the time when the boiler is being worked the hard- 
est. 

The modern double acting steam pump, of which 
there are many different makes to choose from, is 
without doubt the most reliable boiler feeding appli- 
ance and the one best adapted to all circumstances 
and conditions, although it is not economical in the 




DAVIS BELT DRIVEN FEED PUMP. 



use of steam, since the principle of expa-nsion cannot 
be carried out with the pump as with the engine. 

In selecting a feed pump care should be exercised to 
see that it is of the proper size and capacity to supply 
the maximum quantity of water that the boiler can 
evaporate. This may be ascertained by taking into 
consideration the amount of heating surface and the 
required consumption of coal per square foot of grate 
surface per hour. First, take the coal consumption. 
Assume the boiler lo have 30 sq. ft. of grate surface, 



BOILER SETTINGS AND APPURTENANCES 



49 



and that it is desired to burn 15 lbs. of coal per square 
foot of grate per hour, which is a good average with 
the ordinary hand fired furnace using bituminous coal. 




SECTIONAL VIEW OF DIFFERENTIAL VALVE. 

Suppose the boiler is capable of evaporating 8 lbs. of 
water per pound of coal consumed. Then 30 x 15x8 = 
3,600 lbs. of water, evaporated per hour. Dividing 




WORTHINGTON DUPLEX BOILER FEED PUMP. 

3.600 by 62.4 (the weight of a cubic foot of water in 
pounds) gives 57.6 cu. ft. per hour, which, divided by 
60, gives 0.96 cu. ft. per minute. This multiplied by 



50 



ENGINEERING 



1,728 ( number of cubic inches in a cubic foot) gives 
1,659 cu. in. per minute which the pump is required to 
supply. Suppose the pump is to make forty strokes 
per minute, and the length of stroke is five inches. 
Then 1659 -5-40 = 41.47 cu. in. per stroke, which, divided 
by 5 (length of stroke in inches) gives 8.294 sq. in. as 
• the required area of water piston. 8.294-^.7854 = 
10.56, which is the square of the corresponding diam- 




jri m i 



1 — *«* 

jiiiil i J^0S. 




;:'<3i'M 



im. 



Sffli|«l|l§l 

ti MI..W- .. 

iitii a ^ :i ' f 



PHANTOM VIEW OF MARSH INDEPENDENT STEAM PUMP. 



eter, and the square root of 10.56 = 3.25. So, theo- 
retically, the size of the water end of the pump would 
be 3^ in. in diameter by 5 in. stroke; but as it is 
always safer to have a reserve of pumping capacity, 
the proper size of the pump would be 3^ in. in diam- 
eter by 5 in. stroke, with a steam cylinder of 6 or 7 in. 
in diameter. 

There is another rule for ascertaining the size of the 



BOILER SETTINGS AND APPURTENANCES 



51 



feed pump, by taking the number of square feet of 
heating surface in the boiler and allow a pump capacity 
of I cu. ft. per hour for each 15 sq. ft. of heating sur- 
face. Thus, let the total heating surface of the boiler 
be 786 sq. ft. Dividing this by 15 gives 52.4 as the 
number of cubic feet of water required per hour, from 
which the pump dimensions may be found in the same 
way as in the preceding case. 

In figuring on the capacity of a feed pump for a bat- 
tery of two or more boilers, the total quantity of water 
required by all the boilers 
must be taken into consid- 
eration. All boiler-rooms 
should be supplied with at 
least two feed pumps, so 
that if one breaks down 
there may always be an- 
other one available. 

The injector is a reliable 
boiler feeder, and is in fact 
more economical than the 
steam pump, because the 
heat in the steam used is 
all returned to the boiler, 

excepting the losses by radiation. But the disad- 
vantage attending the use of the injector is that it will 
not work well with the feed water at a temperature 
very much in excess of ioo° F. , while a good steam 
pump, fitted with hard rubber valves, will handle water 
at a temperature as high as 200 ° or 208° F. , when the 
water flows to the pump by gravity from a heater, or 
it will raise water from a receiving tank on a short 
suction lift at a temperature of 150 or 160 F. 

Feed Water Heaters. One great source of economy 




AUTOMATIC INJECTOR. 



52 



ENGINEERING 



in fuel is the utilization of all the available exhaust 
steam for heating the feed water before it enters the 
boiler. Of course if the main engine is a condensing 
engine, the exhaust from that source is not directly 
available, except by interposing a closed heater 
between the cylinder and the condenser, or by using 




METROPOLITAN INJECTOR, MODEL O. 



the water of condensation for feeding the boilers. 
This can be clone with safety, provided a surface con- 
denser is used, but with a jet condenser or an open 
heater in which the exhaust mingles with the water, it 
is advisable to have an oil separator to prevent the oil 
from getting into the boilers. 



BOILER SETTINGS AND APPURTENANCES 



,:; 



Exhaust heaters are of two kinds, open and closed. 
In the open heater the exhaust steam mingles directly 
with the water and a portion of it is condensed. A 
well-designed open exhaust heater will raise the tem- 
perature of the water to very 
nearly the boiling point, 212 
F. These heaters should be 
set so that the water will flow 
by gravity from them to the 
feed pump In the closed type 
of exhaust heaters, the exhaust 
steam and the water are kept 
separate. In some styles the 
steam passes through tubes, 
which are surrounded by water, 
while in others the water fills 
the tubes, which are in turn 
surrounded by the steam. In 
either case the water in the 
closed heater is under the. full 
boiler pressure while the feed 
pump is in operation, because 
the heater is between the pump 
and the boiler, while with the 
open heater the pump is be- 
tween the heater and the boiler. 

The saving effected by heat- 
ing the feed water with exhaust 
steam can be easily ascertained 
by the use of a thermometer, 
a steam table, and a simple 
tion. First, find by 




BARAGWANATH STEAM 

JACKET FEED WATER 

HEATER. 



arithmetical calcula- 
thermometer the temperature 
of the water before entering the heater; find its tem- 
perature as it leaves the heater. Next ascertain by 



54 



ENGINEERING 



the steam table the number of heat units above 32 
F. in the water at each of the two temperatures. Sub- 
tract the less from the greater, and the remainder will 
be the number of heat units added to the water by the 
heater. Next find by the table the number of heat 
units above 32 F. in the steam 
at the pressure ordinarily car- 
ried in the boiler, and subtract 
from this the number of heat 
units in the water before it 
enters the heater. The result 
will be the number of heat 
units that would be required to 
convert the water into steam of 
the required pressure, provided 
no heater were used. Then to 
I* find the percentage of saving 
effected by the heater, multiply 
the number of heat units added 
to the water by the heater by 
100, and divide by the number 
of heat units required to con- 
vert the unheated water into 
steam, from the initial temper- 
ature at which it enters the 
heater. 

Example. Assume the boiler 
to be carrying 100 lbs. gauge 
pressure. Suppose the temper- 
ature of the water before entering the heater is 
60 ° F. , and that after leaving the heater its tem- 
perature is 202 F. , what is the percentage of saving 
due to the heater? The solution of the problem is as 
follows: 




INTERIOR VIEW OF OPEN 
HEATER. 



BOILER SETTINGS AND APPURTENANCES 5.5 




56 ENGINEERING . 

Boiler pressure by gauge = ioo lbs. 

Initial temperature of feed water = 6o° F. 

Heated temperature of feed water = 202 F. 

From the steam table (see Chapter IV., Table 5) it 
is found that 

Heat units in water at 202 F. = 170. 7. 

Heat units in water at 6o° F. = 28.01. 

Heat units added to water by heater = 170.7 - 28.01 = 
142.69. 

Heat units in steam at 100 lbs. gauge pressure = 
1 185.0. 

Heat units to be added to water at 6o° F. to make 
steam of 100 lbs. gauge pressure = 1 185.0- 28.01 = 
1156.99. 

Percentage of saving effected by the use of the 

142.69 x 100 

heater = ^ =12.33 per cent. 

1156.99 DD F 

Suppose the coal consumed under this boiler amounts 
to two tons per day at a cost of $3.00 per ton, or a fuel 
cost of $6.00 per day. Then the saving in dollars and 
cents due to the heater in the foregoing example would 
be 12.33 per cent of $6.00, or $0.7398 (74 cents) per 
day. 

Heaters, especially those of the closed type, should 
have capacity sufficient to supply the boiler for fifteen 
or twenty minutes. There would then be a body of 
water continually in the heater in direct contact with 
the heating surface, and as it passes slowly through it 
will receive much more heat than if rushed through a 
heater that is too small. All heaters and feed pipes 
should be well protected by some good insulating 
covering to prevent loss of heat by radiation. In 
some cases the exhaust steam, or a portion of it at 
least, can be used to advantage in an exhaust injector. 



BOILER SETTINGS AND APPURTENANCES 



57 



This device, where it can be used at all, is economical 
in that it not only feeds the boiler, but also heats the 




CLOSED FEED WATER HEATER. 

water without the use of live steam. But it will not 
force the water against a pressure much above 75 lbs. 



58 ENGINEERING 

to the square inch, and if the initial temperature of 
the water is much above 75 F. the exhaust injector 
will not handle it. Heaters which use live steam 
direct from the boilers heat the feed water to a much 
higher temperature, so that they act as purifiers by 
removing a large portion of the scale-forming impu- 
rities before the water enters the boiler. Live steam 
heaters, however, are not to be considered as econo- 
mizers of heat. 

Provisions for Testing. While considering feed pipes 
and other apparatus necessarily appertaining to the 
feeding of boilers, it is well to devote a short space 
also to the fittings and other devices required for suc- 
cessfully conducting tests of the boiler and furnace. 
This subject is mentioned here for the reason that the 
author considers that the necessary fittings and appli- 
ances for making evaporative tests properly belong to, 
and in fact are a part of, the feed piping, and can be 
put in while the plant is being erected at much less 
cost and trouble than if the matter is postponed until 
after the plant is in operation. 

Beginning then at the check valve, there should be a 
tee located in the horizontal section of the feed pipe, 
as near to the check valve as practicable, and between 
it and the feed pump; or a tee can be used in place of 
an ell to connect the vertical and horizontal sections 
of the branch pipe where it rises in front of the boiler. 
One opening of this tee is reduced to V& or }4 in. to 
permit the attachment of a hot water thermometer. 
These thermometers are also made angle-shaped at the 
shank, so that if desired they can be screwed into a tee 
placed in vertical pipe and still allow the scale to 
stand vertical. The thermometer is for the purpose 
of showing at what temperature the feed water enters 



BOILER SETTINGS AND APPURTENANCES 



59 



the boiler during the test, and there- 
fore should be as near the boiler as 
possible. After the test is completed 
the thermometer may be taken out 
and a plug inserted in its place. 

The next requirement will be a de- 
vice of some kind for ascertaining the 
weight of water pumped into the 
boiler during the test. In some well 
ordered plants each boiler is fitted 
with a hot water meter in the feed 
pipe, but as this arrangement is hardly 
within the reach of all, a substitute 
equally as accurate can be made by 
placing two small water tanks, each 
having a capacity of eight or ten cubic 
feet, in the vicinity of the feed pump. 
These tanks can be made of light 
tank iron, and each should be fitted 
with a nipple and valve near the bot- 
tom for connection with the suction 
side of the pump. The tops of the 
tanks may be left open. If an open 
heater is used, and it is possible to 
place the tanks low enough to allow 
a portion of the water from the heater 
to be led into them by gravity, it will 
be desirable to do so. A pipe leading 
from the main water supply, with a 
branch to each tank, is also needed 
for filling them. One of the feed hot water ther- 

r i-i-i 1 ill MOMETER. 

pumps, ot which there should always 

be at least two, as already stated, is fitted with a tee 

in the suction pipe near the pump to receive the pipe 



60 



ENGINEERING 



leading from the tanks. During the test the main suc- 
tion leading to this pump from the general supply 
should be kept closed, so that only .the water that 
passes through the tanks is used for feeding the boiler. 
If the plant be a small one, with but one or two boil- 
ers and only a single feed pump, the latter can be 
made to do duty as a testing pump, because during 
the test there will be no other boilers to feed besides 
the ones under test. 



F££ fLtynT£ t 



HSUPp L y 




TOF&PPUMP 



FIGURE 10. 



If metal tanks are considered too expensive, two 
good water-tight barrels can be substituted. Fig. 10 
will give the reader a general idea of what is needed 
for obtaining the weight of the water by the method 
just described. If a closed heater is used and no other 
boilers are in service during the test, the cold water 
can be measured in the tanks and pumped directly 
through the heater, but if it is necessary to feed other 
boilers besides those under test, then either a separate 



BOILER SETTINGS AND APPURTENANCES 61 

feed pipe must be run to the test boilers, or else hot 
water meters will have to be put into the branch pipes. 

In cases where a separate feed pipe must be put in 
for the test boiler and the water which is used for 
testing cannot be passed through a heater, there 
should be a % or I in. pipe connected to the feed main 
or header and leading to the testing tanks, in order to 
allow a portion of the hot feed water to run into and 
mix with the cold water in the tanks as they are being 
filled, thus partially warming the water before it goes 
to the boiler. 

Heating Surface. The heating surface of a boiler 
consists of that portion of the boiler which is exposed 
to the heat on one side and water on the other. In a 
horizontal boiler of either the flue or tubular type, the 
available heating surface is, first, the lower half of the 
shell; second, the area of the back head below the 
water line minus the combined cross sectional area of 
all the tubes or flues; third, the inside area of the 
flues; fourth, the area of the front head minus the sec- 
tional area of the flues. 

For a fire-box boiler of the vertical type, the area of 
the flue sheets minus the sectional area of the flues, 
plus the area of the fire-box plus the inside area of the 
flues constitutes the heating surface. If the boiler is a 
horizontal internally fired boiler, the heating surface 
will consist of, first, area of three sides of the fire- 
box; second, area of the crown sheet; third, area of 
flue sheets minus sectional area of flues; fourth, inside 
area of the flues. 

In estimating the area of the fire-box, the area of the 
fire door should be subtracted therefrom. If the fire- 
box be circular, as in the case of a vertical boiler, the 
area may be obtained by first finding by measurements 



62 ENGINEERING 

the: diameter, which multiplied by 3.1416 will give the 
circumference. Then multiply this result by the 
height or the distance between the grate bars and 
the flue sheet. In the case of water tube boilers the 
outside area of the tubes must be taken. Two exam- 
ples will be given illustrating methods of calculating 
heating surface: 

First, take a horizontal tubular boiler, diameter 72 
in., length 18 ft., having sixty-two 4^ in. flues; find 
area of lower half of shell. 

Circumference = diameter x 3. 1416 = 18.8496 ft. 

One-half of the circumference multiplied by the 
length = required area. Thus, 18.8496 42x18= 169.64 
sq. ft. 

Next find heating surface of back head below the 
water line. Total area = 72 s x .7854 = 4071.5 sq. in. 
Assume two-thirds of this area to be exposed to the 
heat. 2 /i of 4071.5 = 2714.3 sq. in. From this must be 
deducted the sectional area of the tubes. In giving 
the size of boiler tubes the outside diameter is taken. 
The tubes being 4^2 in.; the area of a circle 4^ in. in 
diameter is 15.9 sq. in. Number of flues, 62 x 15.9 = 
985.8 sq. in. = sectional area of tubes. The heating 
surface of the back head therefore = 2714.3 — 985.8 = 
1728.5 sq. in. Dividing this by 144, to reduce to feet, 
we have 12 sq. ft. 

Next find inside area of tubes. The standard thick- 
ness of a 4)4, in. tube = .134 in. The inside diameter 
therefore will be 4.5 - (2 x . 134) = 4.23 in., and the cir- 
cumference will be 4.23x3.1416=13.29 in., and the 
inside area will be 13.29 x length, 18 ft., = 216 in. 
Thus 216 x 13.29 - 144 = 19.93 sq. ft., inside area of one 
flue. There being 62 flues, the total heating surface of 
tubes is 19.93x62= 1235.66 sq. ft. The heating sur- 



BOILER SETTINGS AND APPURTENANCES 



63 



face of the front head is found in the same manner as 
that of the back head, with the exception that the 
whole area should be figured instead of two-thirds, for 
the reason that the entire surface is exposed to the 
heat, although that portion above the water line may 
be considered as superheating surface. The heating 



surface of front head would be: area 4071 

area of tubes 985.8 = 3085.7 sq. in. = 21.43 

The total heating surface of the boiler 

to be 1438.73 sq. ft, divided up as follows 



Lower half of shel 
Back head, 
Tubes, 
Front head, 



169.64 sq. 
12.00 
1235.66 
21.43 



5 - sectional 

sq. ft. 

is thus found 



ft. 



1438-73 

Next taking a vertical fire-box boiler of the follow- 
ing dimensions: diameter of flue sheet, and also of fire- 
box, 50 in.; height of fire-box above grate bars, 30 in ; 
number of flues, 200; size of flues, 2 in.; length of 
flues, 7 ft. 

First, find heating surface in flue sheet. 

Area of circle, 50 in. in diameter = 1,963.5 sq. in. 

Sectional area of 2 in. flue = 3.14 sq. in., which mul- 
tiplied by 200 = 628 sq. in., total sectional area of 
tubes. The heating surface of one flue sheet therefore 
will be 1,963. 5 - 628 -*- 144 = 9 sq. ft. 

Assuming that the tops of the flues are submerged, 
the area of the top flue sheet will also be 9 sq. ft. 
Then heating surface of flue sheets = 9 x 2 = 18 sq. ft. 

Second, find heating surface of tubes. The standard 
thickness of a 2 in. flue is .095 in. The inside diameter 
will consequently be 2 — (.095 x 2) = 1.8 in., and the 
circumference will be 1.8x3.1416=5.66 in. The 



64 ENGINEERING 

length of the flue being 7 ft., or 84 in., the inside area 
will be 5.66 x 84 -h 144 = 3.3 sq. ft., and multiplying this 
result by 200 we have 20c x 3.3 = 660 sq. ft. as the 
heating surface of the flues. 

Third, find heating surface of the fire-box. Diam- 
eter of fire-box = 50 in., which multiplied by 
3.1416=157.08, which is the circumference. The 
height being 30 in., the total area will be 157.08 x 30 * 
144 = 32.7 sq. ft. Allowing 1 sq. ft. as the area of the 
fire door, will leave 31.7 sq. ft. heating surface of fire- 
box. The heating surface of the boiler will be: 

For the flue sheets, 18 sq. ft. 

For the flues, 660 

For the fire-box, 31.7 

Total, 709-7 

The above methods may be applied in estimating the 
heating surface of any boiler, provided in the case of 
water tube boilers that the outside in place of the 
inside area of the tubes be figured. 

Questions 

1. How should the bridge wall of a horizontal boiler 
be built? 

2. How should the brick work of a boiler be secured 
in order to prevent damage by expansion and contrac- 
tion? 

3. Which end of a horizontal boiler should be the 
lowest, and why? 

4. How should the. water column be located? 

5. How high abo\ r e the top row of tubes should the 
lower gauge cock be? 

6. What is the proper ratio of safety valve area to 
grate surface? 



BOILER SETTINGS AND APPURTENANCES 6,5 

7. Where should the fusible plug be located? 

8. Where should the feed pipe enter the boiler? 

9. Where should the blow off pipe be connected? 

10. What is the most economical device for feeding 
a boiler? 

11. In selecting a feed pump, how may the required 
size of pump be ascertained? 

12. What is the disadvantage in the use of the 
injector for feeding a boiler? 

13. What is gained by using a feed water heater? 

14. How many kinds of exhaust heaters are there? 

15. How may the saving effected by using the 
exhaust steam for heating the feed water be estimated? 

16. What should the capacity of the heater be? 

17. What provision should be made for testing coal 
and other fuel? 

18. What is the heating surface of a boiler? 



CHAPTER III 

BOILER OPERATION 

First care of the engineer on entering his boiler-room — Cleaning 
fires — Fire tools, etc. — Firing — Suggestions as to best method 
of firing — Quantity of air required per pound of coal — Clean- 
ing tubes — Washing out, etc. — Why it is dangerous to cool a 
boiler too quickly — Repairing tubes — Cleaning inside of 
boiler — Pitting — How to feed a boiler — What to do in cases of 
emergency — Connecting with main — Foaming, priming, etc. — 
Safety valve calculations— Rules for safety valve calcula- 
tions — Feed pumps — Care of feed pumps — Directions for set- 
ting steam valves of duplex pumps — Hydraulics for engineers. 

Operation. Having considered in the previous chap- 
ters the principal details in the construction and 
erection of boilers with which the working engineer is 
interested, it is now in order to devote a space to their 
operation. 

Duties. The first act of the careful engineer on 
entering his boiler-room when he goes on duty should 
be to ascertain the exact height of the water in his 
boilers. This he can do by opening the valve in the 
drain pipe of the water column, allowing it to blow 
out freely for a few seconds, then close it tight and 
allow the water to settle back in the glass. This 
should be done with each boiler under steam, not only 
once, but several times during the day. No engineer 
should be satisfied with a general squint along the line 
of gauge glasses, but he should either go himself or 
else instruct his fireman or water tender to make the 
rounds of each boiler and be sure that the water is all 
right. 

60 



BOILER OPERATION 



67 



The next thing to be looked after is the fire. If the 
plant is run continuously clay and night it is the duty 
of the firemen coming off watch to have the fires clean, 
the ash pits all cleaned out, a good supply of coal on 
the floor, and everything in good order for the on 
coming force. A good fireman will take pride in 
always leaving things in neat shape for the man who 
is to relieve him. 

Cleaning Fires. With some varieties of coal this is 




lahman's grate. 



a comparatively easy task, especially if the boilers are 
fitted with shaking grates. With a coal that does not 
form a clinker on the grate bars, the fires can be kept 
in good condition by cleaning them twice or three 
times in twenty-four hours, as the larger part of the 
loose ashes and noncombustible can be gotten rid of 
by shaking the grates and using the slice bar at inter- 
vals more or less frequent; but such coals are generally 
considered too expensive to use in the ordinary manu- 
facturing plant, and cheaper grades are substituted. 



68 



ENGINEERING 



Fire Tools. For cleaning fires successfully and 
quickly the following tools should be provided: a slice 
bar, a fire hook, a heavy iron or steel hoe, and a light 
hoe for cleaning the ash-pit. It is unnecessary to 
describe these tools, as they are familiar to all 
engineers. A suggestion as to the kind of handles 
with which they should be fitted may be of benefit. 
The working ends of the aforesaid tools having been 
made and each welded to a bar of I ori^ in. round 




MARTIN ANTI-FRICTION ROCKING GRATES. 



iron and 10 or 12 in. long, take pieces of 1 or 1% in. 
iron pipe cut to the length desired for the handles and 
weld the shanks of the tools to them. To the other 
end of the pipe weld a handle made of round iron 
somewhat smaller than the shank. By using pipe 
handles the weight of the tools is considerably lessened, 
and they will still be sufficiently strong. The labor of 
cleaning the fire will thus be greatly lightened. When 
a fire shows signs of being foul and choked with 



BOILER OPERATION 69 

clinker, preparations should be made at once for clean- 
ing it by allowing one side to burn down as low as pos- 
sible, putting fresh coal on the other side alone. When 
the first side has burned as low as it can without 
danger of letting the steam pressure fall too much, 
take the slice bar and run it in along the side of the 
furnace on top of the clinker and back to near the 
bridge wall, then using the door jamb as a fulcrum, give 
it a quick strong sweep across the fire and the greater 
part of the live coals will be pushed over to the other 
side. What remains of the coal not yet consumed can 
be pulled out upon the floor with the light hoe and 
shoveled to one side, to be thrown back into the 
furnace after the clinker is taken out. Having now 
disposed of the live coal, take the slice bar and run it 
along on top of the grates, loosening and breaking up 
the clinker thoroughly, after which take the heavy hoe 
and pull it all out on the floor. A helper should be 
ready with a pail of water, or, what is still better, a 
small rubber hose connected to a cold water pipe run- 
ning along the boiler fronts for this purpose, and put 
on just enough water to quench the intense heat of the 
red hot clinker as it lies on the floor. ' When the 
grates are cleaned, close the door, and with the slice 
bar in the other side push all the live coal over to the 
side just cleaned, where it should be leveled off and 
• fresh coal added. After this has become ignited, treat 
the other side in the same way. An expert fireman 
will thus clean a fire with very little loss in steam 
pressure, and practically no waste of coal. 

Firing. No definite set of rules for hand firing can 
be laid down that will be suitable for all steam plants, 
or for the many different kinds of coal used. Some 
kinds of coal need very little stirring or slicing, while 



70 ENGINEERING 

others that have a tendency to coke and form a crust 
on top of the fire need to be sliced quite often. 

Every engineer, if he is at all observant, should be 
able to judge for himself as to the best method of 
treating the coal he is using, so as to get the most 
economical results. A few general maxims may be 
laid down. First, keep a clean fire; second, see that 
every square inch of grate surface is covered with a 
good live fire; third, keep a level fire, don't allow hills 
and valleys and yawning chasms to form in the fur- 
nace, but keep the fire level; fourth, when cleaning the 
fire always be sure to clean all the clinkers and dead 
ashes away from the back end of the grates at the 
bridge wall, in order that the air may have a free pas- 
sage through the grate bars, because this is one of the 
best points in the furnace for securing good combus- . 
tion provided the bridge wall is kept clean from the 
grates up. By keeping the back ends of the grate bars 
and the face of the bridge wall clean, the air is per- 
mitted to come in contact with the hot fire brick, and 
thus one of the greatest aids to good combustion is 
utilized. Don't allow the fire to become so deep and 
heavy that the air cannot pass up through it, because 
without a good supply of air good combustion is 
impossible. When the chimney draft is good the 
quantity of cold air admitted underneath the grate 
bars may be easily regulated by leaving the ash-pit 
doors partly open. The amount of opening required 
can be ascertained by a little experimenting and 
depends upon the intensity of the draft and the condi- 
tion of the fire. With a clean, light fire and the air 
spaces in the grates free from dead ashes, a slight 
opening of the ash-pit doors will suffice to admit all 
the air required beneath the grates. But if the fire is 



BOILER OPERATION 71 

heavy and the grates are clogged, a larger opening 
will be necessary. In firing bituminous coal contain- 
ing a large percentage of volatile (light or gaseous 
matter) the best results can be obtained by leaving the 
fire doors slightly open for a few seconds immediately 
after throwing in a fresh fire. The reason for doing 
this is that the volatile matter in the coal flashes into 
flame the instant it comes in contact with the heat of 
the furnace, and if a sufficient supply of oxygen is not 
present just at this particular time the combustion will 
be imperfect and the result will be the formation of 
carbon mon-oxide or carbonic oxide gas, anct the loss 
of about two-thirds of the heat units contained in the 
coal. This loss can be guarded against in a great 
measure by a sufficient volume of air, either through 
the fire doors directly after putting in a fresh fire, or, 
what is still better, providing air ducts through the 
bridge wall or side walls which will bring the air in on 
top of the fire. Each pound of coal requires for its 
complete combustion 12 lbs. or about 150 cu. ft. of air, 
and the largest volume of air is needed just after fresh 
coal has been added to the fire. 

Cleanli?iess. In order to get the best results great 
care should be taken that the tubes be kept clean and 
free from soot. Especially does this apply to horizon- 
tal return tubular boilers, for the reason that when the 
tubes become clogged with soot the efficiency of the 
draft is destroyed and the steaming capacity of the 
boiler is greatly reduced. Soot not only stops the 
draft, but it is a non-conductor of heat. In some 
batteries of boilers where an inferior grade of coal is 
used and the draft is poor, it is absolutely necessary 
to scrape or blow the tubes at least once a day in 
order to enable the boilers to generate sufficient steam. 



72 ENGINEERING 

As to the process of cleaning there are various 
devices on the market, both for blowing the soot out 
by means of a steam jet and also for scraping the 
inside of the tubes. The steam jet, if properly made 
and used with a high pressure and dry steam, does 
very satisfactory work, but it should not be depended 
upon exclusively to keep the tubes clean, because in 
process of time a "scale will form inside the tubes that 
nothing but a good scraper will remove. For that 
reason it is good practice to use the scraper two or 
three times a week at least. When the boiler is 
cooled down for washing out, the bottom of the shell 
should be cleaned of all accumulations of dust and 
ashes, the combustion chamber back of the bridge wall 
cleaned out, and the back flue sheet or head swept off 
and examined, and if there is a fusible plug in the back 
head the scale should be scraped from it, both inside 
and outside the boiler, because if it is covered with 
scale neither the water nor the heat can come in con- 
tact with it, and it will be non-effective. 

Washing Out. The length of time that a boiler can 
be run safely and economically after having been 
washed out depends upon the nature of the feed water. 
If the water is impregnated to a considerable extent 
with scale forming matter, the boiler should be washed 
out every two weeks at the least, and in. some cases of 
particularly bad water it becomes necessary to shorten 
the time to one week. To prepare a boiler for washing 
the fire should be allowed to burn as low as possible 
and then be pulled out of the furnace, the furnace 
doors left slightly ajar and the damper left wide open 
in order that the walls may gradually cool. It is as 
bad a practice to cool a boiler off too suddenly as it is 
to fire it up too quick, because the sudden change of 



BOILER OPERATION 16 

temperature either way has an injurious effect on the 
seams, contracting or expanding the plates, according 
as it is cooled or warmed, and thus creating leaks and 
very often small cracks radiating from the rivet holes, 
and becoming larger with each change of temperature, 
until finally the strength of the seam is destroyed and 
rupture takes place. After the boiler has become 
comparatively cool and there is no pressure indicated 
by the steam gauge the blow off cock may be opened 
and the water allowed to run out. The gauge cocks 
and also the drip to the water column should be left 
open to allow the air to enter and displace the water. 
Otherwise there will be a partial vacuum formed in the 
boiler and the water will not run out freely. 

A boiler should not be blown out, that is, emptied 
of water while under pressure. The sudden change of 
temperature is sure to have a bad effect upon the 
sheets and seams. Suppose for instance that all the 
water is blown out of a boiler under a pressure of 
20 lbs. by the steam gauge. The temperature of steam 
at 20 lbs. is 260 F., and it may be assumed that the 
metal of the boiler is at or near that temperature also. 
Assume the temperature of the atmosphere in the 
boiler-room to be 6o° F. There will then be a range 
of 260 — 6o° = 200 temperature for the boiler to pass 
through within a short time, which will certainly have 
a bad effect, and besides this the boiler shell will be so 
hot that the loose mud and sediment left after the 
water has run out is liable to be baked upon the 
sheets, making it much harder to remove. 

While inside the boiler the boiler washer should 
closely examine all the braces and stays, and if any are 
found loose or broken they should be repaired at once 
before the boiler is used again. The soundness of 



74 ENGINEERING 

braces, rivets, etc., can be ascertained by tapping 
them with a light hammer. 

Renewing T?tbes. As it is practically impossible to 
prevent scale from forming on the outside of the tubes 
of horizontal tubular boilers unless the feed water is 
exceptionally good, and as the tubes will in course of 
time become leaky where they are expanded into the 
heads, the engineer if he has a battery of two or more, 
should take advantage of the first opportunity that 
presents itself to take out of service the boiler that 
shows the most signs of deterioration and take out the 
tubes, and after cleaning them of scale by scraping and 
hammering or rolling in a tumbling cylinder, he should 
select those that are still in good condition and have 
them pieced out at the ends, making them almost as 
good as new. 

The flues being out of the boiler will give the boiler 
washer a good opportunity to thoroughly clean the 
inside also, and if there are any loose rivets they 
should be replaced and leaky or suspicious looking 
seams chipped and caulked. If there are indications 
of corrosion or pitting, a stiff paste or putty made of 
plumbago mixed with a small proportion of cylinder 
oil may be applied to the affected parts with good 
results. 

Feed Water. There is no steam plant of any conse- 
quence that does not have more or less exhaust steam 
or returns from a steam heating system which can be 
utilized for heating the feed water before it enters the 
boiler. Cold water should never be pumped into a 
boiler that is under steam when it is possible to 
prevent it. 

In feeding a boiler the speed of the feed pump 
should be so gauged as to supply the water just as fast 



BOILER OPERATION 75 

as it is evaporated. The firing can then be even and 
regular. 

If the supply of feed water should suddenly be cut 
off, owing to breakage of the pump or bursting of a 
water main, and no other source of supply was avail- 
able, the dampers should be immediately closed, or if 
there should be no damper in the breeching, the draft 
may be stopped by opening the flue doors. The fires 
should then be deadened by shoveling wet or damp 
ashes in on top of them, or if the ashes cannot be 
readily procured, bank the fires over with green coal 
broken into fine bits. This, with the draft all shut off. 
will deaden the fires, while the engine still running 
will gradually use up the extra steam. If the water 
should get dangerously low in the boilers the fires 
may be pulled, provided they have become deadened 
sufficiently, but they should never be pulled while they 
are burning lively, because the stirring will only serve 
to increase the heat and the danger will be aggra- 
vated. 

Comiecting a Recently Fired Up Boiler. After a boiler 
has been washed out, filled with water, and fired up, 
the next move is to connect it with the main battery. 
The steam in the boiler to be connected having been 
raised to the same pressure as that in the battery, the 
connecting valve should be opened slightly, just 
enough to permit a small jet of steam to pass through, 
which can be heard by placing the ear near the body of 
the valve. This jet of steam may be passing from the 
battery into the newly connected boiler or vice versa. 
Whichever way it passes, the valve should not be 
opened any farther until the flow of steam stops, 
which will indicate that the pressure has been equal- 
ized. It will then be found that the valve will move 



70 ENGINEERING 

much easier and it may be gradually opened until it is 
wide open. 

Foaming. Water carried with the steam from the 
boiler to the engine, even if in small quantities, is very 
detrimental to the successful operation of the engine, 
as it washes the oil from the walls of the cylinder, 
thereby increasing the friction, and unless a plentiful 
supply of oil is entering the cylinder cutting of the 
piston rings will take place. There is also danger of 
breaking a cylinder head or of bending the piston rod 
if the water comes in too large quantities. 

There are certain kinds of water which have a natu- 
ral tendency to foam, especially such as contain con- 
siderable organic matter, and the more severe the 
service to which the boiler is put the more will the 
water foam, until it is practically impossible to locate 
the true level of the water in the boilers, and the only 
recourse the water tender has is to keep his feed pump 
running at such a speed as will in his judgment supply 
the water as fast as it goes out of the boilers. It is a 
dangerous condition to say the least, and the only 
remedy for it is either a change to a different kind of 
water, or if this is not possible, then an increase in 
the number of boilers, which would make it possible 
to supply sufficient steam for the engine without being 
compelled to fire the boilers so hard. 

Pi r imi?ig. By which is meant the carrying over of 
water in the form of fine spray mingled with the 
steam, is not so dangerous as foaming and yet it 
causes much loss in the efficiency of a boiler or 
engine. It can be prevented to a large extent by 
placing a baffle plate in the steam space of the boiler 
directly under the dome or outlet to the connection 
with the steam main. 



BOILER OPERATION 77 

Safety Valves. Rules are given in Chapter II. for 
guidance in making calculations relating to spring pop 
valves, which are now almost universally used on 
boilers, and which, without doubt, are the most reliable 
appliance for relieving a boiler of surplus steam; 

A short space will be devoted to the consideration 
of the lever safety valve also, as it may be of interest 
to some students. 

The U. S. marine rule for lever valves is here 
repeated: "Lever safety valves to be attached to 
marine boilers shall have an area of not less than one 
square inch to every two square feet of grate surface in 
the boiler, and the seats of all such safety valves shall 
have an angle of inclination of 45 to the center line 
of their axis." 

In order to arrive at accurate results in lever safety 
valve calculations it is necessary to know first the num- 
ber of pounds pressure exerted upon the stem of the 
valve by the lever itself, irrespective of the weight, 
also the weight of the valve and stem, as all these 
weights together with the weight of the ball suspended 
upon the lever tend to hold the valve down against 
the pressure of the steam. The effective weight of the 
lever can be ascertained by leaving it in its position 
attached to the fulcrum and connecting a spring bal- 
ance scale to it at the point where it rests on the valve 
stem. The weight of the valve and stem can also be 
found by means of the scale. When the above weights 
are known, together with the weight at the end of the 
lever and its distance from the fulcrum, also the area 
of the valve and its distance from the fulcrum, the 
pressure at which the valve will blow can be found by 
the following rules: 

Rule 1. Multiply the weight by its distance from the 



78 ENGINEERING 

fulcrum. Multiply the weight of the valve and lever 
by the distance of the stem from the fulcrum and add 
this to the former product. Divide the sum of the 
two products by the product of the area of the valve 
multiplied by the distance of its stem from the 
fulcrum. The result will be pressure in pounds per 
square inch required to lift the valve. 

Example. Diameter of value, 3 in. 

Distance of stem from fulcrum, 3 in. 

Effective weight of lever, valve and stem, 20 lbs. 

Weight of ball, 50 lbs. 

Distance of ball from fulcrum, 30 in. 

Required pressure at which the valve will blow off, 
50 x 30 + 20 x 3 = 1560. 

Area of valve, 7.0686 x 3 = 21.2058. 

1560 -*- 21.2058 = 73-57 lbs. pressure. 

When the pressure at which it is desired the valve 
should blow off is known, together with the weights of 
all the parts, the proper distance from the fulcrum at 
which to place the weight is ascertained by'Rule 2. 

Ride 2. Multiply the area of the valve by the pres- 
sure and from the product subtract the effective weight 
of the valve and lever. Multiply the remainder by the 
distance of the stem from the fulcrum and divide hy 
the weight of the ball. The quotient will be the 
required distance. 

Example. Area of valve, 7.07 sq. in. 

To blow off at 75 lbs. 

Effective weight of lever and valve, 20 lbs. 

Weight of ball, 50 lbs. 

Distance of valve stem from fulcrum, 3 in. 

7.07 x 75 - 20 = 510.25. 

510.25x3^-50 = 30.6 in., distance from fulcrum at 
which to place the ball. 



BOILER OPERATION 79 

When the pressure is known, together with the 
distance of the weight from the fulcrum, the weight ot 
the ball is obtained by Rule 3. 

Rule j. Multiply the area of the valve by the pres- 
sure and from the product subtract the effective weight 
of the lever and valve. Multiply the remainder by 
the distance of the stem from the fulcrum and divide 
by the distance of the ball from the fulcrum. The 
quotient will be the required weight. 

Example. Area of valve, . . . . 7.07 sq. in. 

Pressure in pounds per square inch, . . 80 lbs. 

Effective weight of lever and valve, . . 20 lbs. 

Distance of stem from fulcrum, .... 3 in. 

Distance of weight from fulcrum, ... 30 in. 

7.07 x 80-20 = 545.6. 

545.6 x 3 -i- 30 = 54.56 lbs., weight of ball. 

Safety valves, especially those of the lever type, are 
liable to become corroded and stick to their seats if 
allowed to go any great length of time without blow- 
ing. Therefore it is good practice to raise the steam 
pressure to the blowing off point at least two or three 
times a week, or oftener, for the purpose of testing 
the valve. If it opens and releases the steam at the 
proper point all is well, but if it does not, it should be 
looked after forthwith. Generally the mere raising of 
the lever by hand, or a few taps with a hammer it it 
be a pop valve, will free it and cause it to work all 
right again; but if this treatment has to be resorted to 
very often the valve should be taken down and over- 
hauled. In too many steam plants not enough import- 
ance is attached to the safety valve. The fact is, 
it is one of the most useful and important adjuncts of 
a boiler, and if neglected serious results are sure to 
follow. 



80 ENGINEERING 

Feed Pumps. A good engineer will always take a 
pride in keeping his feed pump in good condition, and 
if he has two or more of them, which every steam 
plant of any consequence should have, he will have an 
opportunity to keep his pumps in good shape. The 
water pistons of most boiler feed pumps are fitted to 
receive rings of fibrous packing. The best packing for 
this purpose and one that will stand both hot and cold 
water service is made of pure canvas cut in strips of 
the required width, y 2 , $/&, Y\ in., etc., and laid 
together with a water proof cement having the edges 
for the wearing surface. This packing is called square 
canvas packing, and can be purchased in any size 
required for the pump. The size is easily ascertained 
by placing the water piston, minus the follower plate, 
centrally in the water cylinder and measuring the 
space between the piston and cylinder walls. This 
packing should not be allowed to run for too long a 
time before renewing, for the reason that pieces of it 
are liable to become loose and be forced along with 
the feed water on its way to the boiler and lodge 
under the check valve, holding it open and causing no 
end of trouble. If the feed pump has to handle hot 
water, or has to lift the water several feet by suction, 
the packing rings should be looked after at least once 
a month. 

Hard rubber valves are, all things considered, the 
best for a boiler feed pump, as they are not affected 
by hot water and do not hammer the seats like metallic 
composition valves do. Every boiler feed pump 
should be fitted with a good sight-feed lubricator for 
cylinder oil. The steam valve mechanism of a steam 
pump is very sensitive and delicate and requires good 
lubrication in order to do good work. In too many 



BOILER OPERATION 81 

cases feed pumps are fitted with an old style cylinder 
oil cup and there is generally more oil on the outside 
of the valve chest than there is inside, while the valve 
is bulldozed into working by frequent blows from a 
convenient club. 

The steam valves of all steam pumps are adjusted 
before they are sent out from the factory, and most of 
them are arranged so that the stroke may be 
shortened or lengthened as the engineer desires. It 
is best as a rule to allow a pump to make as long a 
stroke as it will without striking the heads, because 
then the parts are worn evenly. 

Sometimes an engineer is called upon to set the 
valves of a duplex pump which have become disar- 
ranged. In such a case he should proceed as follows: 
Place both pistons exactly at mid-stroke. This may 
be done in two ways. First, by dropping a plummet 
line alongside the levers connecting the rock shafts 
with the spools on the piston rods. Then bring the 
rods to the position where the centers of the spools 
will be in a vertical line with the centers of the rock 
shafts. 

The second method is to move the piston to 
the extreme end of the stroke until it comes in contact 
with {he cylinder head. Then mark the rod at the 
face of the stuffing box gland. Next move the piston 
to the other end of the stroke and mark the rod at the 
opposite gland. Now make a mark on the rod exactly 
•half way between the two outside marks and move the 
piston back until the middle mark is at the face of the 
gland and the piston will be at mid-stroke. Having 
placed both pistons at mid-strike, remove the valve 
chest covers and adjust the valves in their central posi- 
tion, viz., so that they cover the steam ports. The 



82 ENGINEERING 

valve rod being in position and connected to the 
rocker arm by means of the short link, the nut or nuts 
securing the valve to the rod should be so adjusted as 
to be equidistant from the lugs on the valve, say fa or 
yi of an inch according to the amount of lost motion 
desired, which latter factor governs the length of 
stroke in some makes of duplex pumps, while in 
others it is controlled by tappets on the valve rod 
outside of the valve chest. Care should be taken 
while making these adjustments that the valve be 
retained exactly in its central position. 

Having set the valves correctly, move one of the 
pistons far enough from mid-stroke to get a small 
opening of the steam port on the opposite side, then 
replace the valve chest covers and the pump will be 
ready to run. As these valves are generally made 
without any outside lap, a slight movement of one of 
the pistons in either direction from its central position 
will suffice to uncover one of the ports on the other 
cylinder sufficiently to start the pump. 

Sometimes duplex pumps "work lame," that is, 
one piston will make a quick full stroke while the 
other piston will move very slowly and just far enough 
to work the steam valve of the opposite side. In the 
majority of cases this irregular action is due to 
unequal friction in the packing of the rods, or the 
packing rings on one of the pistons may be worn out. 

If one side of a duplex pump becomes disabled from 
any cause, as breaking of piston rod in the water 
cylinder, for instance, which is liable to happen, the 
pump may still be operated in the following manner 
until duplicate parts to replace the broken ones have 
been .secured. Loosen the nuts or tappets on the 
valve stem of the broken side and place them far 



BOILER OPERATION 83 

enough apart so that the steam valve will be moved 
through only a small portion of its stroke, thereby 
admitting only steam enough to move the empty 
steam piston and rod, and thus work the steam valve 
of the remaining side. The packing on the broken 
rod should be screwed up tight, so as to create as 
much friction as possible; there being no resistance in 
the water end. In this way the pump may be oper- 
ated for several days or weeks and thus prevent a shut 
down. 

Hydraulics for Engineers. Among the many difficult 
problems that are continually coming up for engineers 
to solve, there is none more perplexing than the cor- 
rect calculation of the quantit}' of water which will be 
discharged in a given time from pipes of various sizes 
and under the many different heads or pressures. 
Problems in hydraulics, as given by the majority of 
writers on engineering, are usually in elaborate alge- . 
braical equations, which, to the ordinary working 
engineer, are very perplexing, at least the author has 
found them to be so in his experience. Therefore 
with a view of assisting his brother engineers in the 
solution of problems along this line which they may 
be called upon to solve, the author has spent consider- 
able time and labor in searching for and compiling a 
few rules and examples for hydraulic calculations in 
plain arithmetic which he hopes may be of benefit. . 

First, to find velocity of flow in the pump, or in 
other words, piston speed. 

Rule. Multiply number of strokes per minute by 
length of stroke in feet, or fractions thereof. 

Second, the velocity of flow in the discharge pipe 
is in inverse ratio to the squares of the diameters of 
the pipe and the water cylinder of pump. 



84 ENGINEERING 

Thus, a pump cylinder is 6 in. in diameter, and the 
piston speed is ioo ft. per minute; the discharge pipe 
being 3 in. in diameter. What is the velocity of. flow 
in the pipe? 

Exajnple. 3^=4. In this case the velocity in the 
pipe is four times that in the pump, and 100 x 4 = 400 ft. 
per minute, velocity for water in the discharge pipe. 

Third, to find velocity in feet per minute necessary 
to discharge a given quantity of water in a given 
time. 

Rule. Multiply the number of cubic feet to be dis- 
charged by 144 and divide by area of pipe in inches. 

Fourth, to find area of pipe when the volume and 
velocity of water to be discharged are known. 

Rule. Multiply volume in cubic feet by 144 and 
divide by the velocity in feet per minute. 

Fifth, one of the first requisites in making correct 
calculations of the quantity of water discharged from 
any sized pipe is to obtain the velocity of flow per 
second. There are several rules for doing this, among 
which the following appear to be the plainest and 
most simple: 

Rule 1 Multiply the square root of the head in 
inches by the constant 27.8. For instance, assume 
the head to be 100 ft. = 1200 in. The square root of 
1200 is 35 nearly, then 35 x 27.8 = 973 in. = 81 ft. per 
second velocity. 

Rule 2. Multiply the square root of the head in feet 
by the constant 8, as follows: The square of 100= 10 
and 10 x 8 = 80 ft. velocity per second. 

Rule j. Multiply twice the acceleration of gravity 
by the head in feet and extract the square root of 
product. The acceleration of gravity may be consid- 
ered the constant number 32, neglecting decimals. 



BOILER OPERATION 85 

32 x 2 x 100 = 6400. Square root of 6400 = 80 ft. per 
second. 

In many instances it is more convenient to use the 
pressure in pounds per square inch as shown by gauge 
instead of the height or head, and we can then apply 
Rule 4. 

Rule 4. Multiply the square root of the pressure in 
pounds per square inch by the constant number 12.16 
as follows: Pressure due to 100 ft. head = 44 lbs., 
nearly. Square root of 44 = 6.6, which multiplied by 
12.16 = 80.2 ft. velocity per second. 

Having ascertained the velocity of flow, we may 
now proceed to calculate the weight of water in 
pounds per second discharged from any size of pipe, 
neglecting for the time being the loss in pressure 
caused by friction from elbows and bends in the pipe 
and also the peculiar shape assumed by a stream of 
water flowing through pipes or conduits when there is 
no resistance except the pressure of the atmosphere 
and friction caused by long distance transmission. 

We will take for our calculation a four-inch pipe 
from which the water has a free flow under a head of 
100 ft., which gives a velocity of 80 ft. per second. 

Rule 5. Divide the velocity in feet per second by the 
constant 2.3, and multiply the quotient by the area of 
discharge pipe in square inches. 80 + 2.3 = 34.7. 
Now the area of a four-inch pipe is 12.57 sq. in., and 
34.7 x 12.57 = 436 lbs. discharged per second. 

In order to get the matter clearly before us, let us 
assume that we have a section of four-inch pipe just 
80 ft. in length and that it lies in a horizontal position 
and is filled solidly full of water. It will contain area, 
12.57 sq. in. x length, 960 in. = 12,067.2 cu. in. of water, 
and as one pound of water occupies a space of 



80 ENGINEERING 

2j.j cu. in. , we therefore have 1,2067.2 -f- 27.7 = 436 lbs. 
of water, and at a velocity of 80 ft. per second our 
pipe will be emptied and refilled continuously each 
second. We have also Rule 6 to find the number of 
cubic feet discharged per minute when the velocity 
per minute is known. 

Rule 6 Multiply the area of pipe in square inches 
by the velocity in feet per minute and divide by the 
constant 144. 

Example. Area of 4 in. pipe = 12.57 sq. in. Velocity 
of flow = 80 ft. per second = 4,800 ft. per minute. Then 
i2^x4 i 80o = 4I9 cu> ft _ per m i nut e = 6.99 cu. ft. per 
second, which multiplied by 62.3 lbs. (weight of 1 cu. 
ft.) = 435.4 lbs. per second. 

As stated before, no allowance is made by the above 
rules for friction or other retarding influences, but foi 
ordinary purposes in connection with a steam plant a 
deduction of 25 per cent, is probably sufficient. Of 
course if the water is being discharged into an elevated 
tank or against direct pressure of any kind, the resist- 
ance in pounds per square inch or the height in feet 
must be deducted from the impelling pressure or head. 
Let us assume, for instance, that our 4 in. pipe is dis- 
charging water into a tank at an elevation of 75 ft. 
above the level of the pump, and that to reach the 
tank requires 100 ft. of pipe with two 90° ells and one 
straight-way valve. We wish to discharge 500 gal. 
per minute into the tank ana will therefore require a 
velocity of about 13 ft. per second, which will necessi- 
tate a pressure of a little more than 1 lb. per square 
inch to be maintained at the pump over and above all 
resistance. Now the resistance to be overcome in this 
case will be: 



BOILER OPERATION 87 

Pressure per square inch due to 75 ft. head, 32.5 lbs. 
Friction loss due to length of pipe and velocity, 7.43 ' 
Friction loss due to two 90 ells, 2.16 ' 

Friction loss due to straight way valve, .2 

Total, 42.29 lbs. 
Requiring a pressure of say 43 lbs. per square inch, 
or about the equivalent of 100 ft. head at the pump. 

Again, suppose that in place of the elevated tank 
we have 1,000 ft. of 8 in. horizontal pipe with a 4 in. 
delivery at the end farthest from the pump, and three 
branch pipes each 100 ft. long and 4 in. in diameter 
with one 90 ell and one straight-way valve, connected 
at intervals to the 8 in. main, and it is required to dis- 
charge in all 1,000 gals, per minute, or at the rate of 
250 gals, per minute for each 4 in. delivery. The 
friction loss for each 100 ft, in length of 8 in. pipe at 
a velocity of 13 ft. per second is .94 lbs., and for each 
100 ft. of 4 in. pipe it is 1.89 lbs. Likewise the 
friction loss for each- 90 ell is 1.08 lbs., and for a 
straight way valve .2 lbs., at the above velocity. The 
total resistance therefore to be overcome is as follows: 
For 1,000 ft. of 8 in. pipe, .94 lbs. x 10 = 9.4 lbs. 
For 300 ft. of 4 in. pipe, 1.89 lbs. x 3 = 5.67 
For four 90 ells, 1.08 lbs. x 4 = 4.32 " 

For four straight-way valves, .2 lbs. x 4= .8 

Total, 20.19 l° s - 
Consequently the pressure required at the pump will 
be about 22 lbs. per square inch, equal to a head of 
50 ft. 

Questions 

1. What should be the first care of an engineer on 
entering his boiler room when he goes on watch? 



88 ENGINEERING 

2. What is one of the duties of the fireman before 
coming off watch? 

3. Name the various tools necessary for cleaning 
fires properly. 

4. Describe the operation of cleaning fires. 

5. What general rules should be observed in firing? 

6. How may the best results be obtained in firing 
bituminous coal? 

7. What will be the result if a sufficient supply of 
oxygen is not admitted to the furnace? 

8. What quantity of air (cubic feet or pounds 
weight) is required for the complete combustion of 
one pound of coal? 

9. Suppose there is a fusible plug in jthe boiler and 
it becomes covered with scale, what will be the result? 

10. How long may a boiler be run safely after wash- 
ing it out? 

11. What should be done with a boiler in order to 
prepare it for washing out? 

12. What effect does the too sudden cooling off or 
firing up of a boiler have upon the seams? 

13. What other bad result takes place within the 
boiler when it is emptied of water while hot? 

14. What should be done with tubes that have 
become badly scaled? 

15. How fast should the feed water be supplied? 

16. What should be done in case the supply of feed 
water be cut off suddenly? 

17. What is the proper method of connecting a 
recently fired up boiler to the main header? 

18. What are some of the dangerous results of 
foaming? 

19. What can be done to prevent or at least to 
modify foaming in boilers? 



BOILER OPERATION 89 

20. Which are the most reliable pop valves or lever 
safety valves? 

21. What is the rule regulating the area of lever 
safety valves? 

22. What two factors must first be known before cor= 
rect calculations can be made as to the weight and posi- 
tion of the ball on a lever safety valve? 

23. How may the effective weight of the lever and 
that of the valve and stem be found? 

24. When the area in square inches of the valve, the 
weight of the valve and stem, the effective weight of 
the lever, the weight of the ball and its distance from 
the fulcrum are known, how is the pressure at which 
the valve will blow off ascertained? 

25. When the pressure at which the valve should 
blow off is known, together with the weights of all the 
parts, how may the distance the ball should be from 
the fulcrum be ascertained? 

26. When the pressure is known, together with the 
distance of the ball from the fulcrum, how is the 
weight of the ball found? 

27. What should be done with a safety valve in 
order to keep it in good working condition? 

28. Describe the process of setting the steam valves 
of a duplex pump. 

29. How may a duplex pump be operated in case 
one of the water pistons becomes disabled? 

30. How is the velocity of flow or piston speed per 
minute of a pump ascertained? 

31. The piston speed being known, how is the velo- 
city of flow in the discharge pipe found? 

32. When it is required to discharge a certain quantity 
of water from a given size of pipe in a given time, how 
may the velocity of flow in feet per minute be found? 



90 ENGINEERING 

33. When the volume of water to be discharged and 
the velocity of flow are known, how is the area of the 
pipe obtained? 

34. What is meant by "acceleration of gravity," and 
what constant number represents it in connection with 
hydraulics? 

35. What per cent, of allowance is ordinarily made 
for friction in water pipes? 



CHAPTER IV 

COMBUSTION -WATER— STEAM 

Combustion — Composition of air — Carbon — The principal constit- 
uent of fuels — Hydrogen, its nature and heating value — 
Table, giving analysis of various coals — Process of combus- 
tion described — Quantity of air required — Furnace tempera- 
ture — How to utilize the heat in the escaping gases — Heat, 
what it is and how produced — Joule's researches — The heat 
unit — Specific heat — Sensible heat and latent heat — Experi- 
ments of Professor Black — Total heat of evaporation — Water, 
its composition, nature, etc. — Steam, its expansive nature, 
temperature, etc. — Saturated steam, etc. — Total heat of 
steam — Density of steam. 

Combustion. The subject of the combustion of fuels 
being one in which every engineer is vitally interested, 
it is proper that its leading features and principles be 
discussed. One of the main factors in the combustion 
of coal is the proper supply of air. Air is composed 
of two gases, oxygen and nitrogen, in the proportion, 
by volume, of 21 per cent, of oxygen and 79 per cent, 
of nitrogen, or by weight, 23 per cent, of oxygen and 
J7 per cent, of nitrogen. 

The composition of pure dry air, as given by Kent 
in Steam Boiler Economy, is as follows: 

By volume, 20.91 parts O. and 79.09 parts N. 

By weight, 23.15 parts O. and 76.85 parts N. 

Air is a mixture and not a chemical combination of 
these two elements. The principal constituent of coal 
and most other fuels, whether solid, liquid or gaseous, 
is carbon. Hydrogen is a light combustible gas and 
combined either with carbon or with carbon and 
91 



92 



ENGINEERING 



oxygen, in various proportions, is also a valuable con- 
stituent of fuels, notably of bituminous coal. The 
heating value of one pound of pure carbon is rated at 
14,500 heat units, while one pound of hydrogen gas 
contains 62,000 heat units. 

Analysis of coal shows that it contains moisture, 
fixed carbon, volatile matter, ash and sulphur in vari- 
ous proportions according to the quality of the coal. 
The following table deduced from a few of the many 
valuable tables of analysis of the coals of the United 
States, as given by Mr. Kent, will show the composi- 
tion of the principal bituminous coals in use in this 
country for steam purposes. Two samples are selected 
from each of the great coal producing states, with the 
exception of Illinois, from which four were taken. 

Table 2 



State 


Kind of Coal 


Moist- 
ure 


Vola- 
tile 
Matter 


Fixed 
Carbon 


Ash 


Sul- 
phur 


Pennsylvania 


Youghiogheny 


1.03 


36.49 


59.05 


2.61 


0.81 


" 


Connellsville 


1.26 


30.10 


59.61 


8.23 


0.78 


West Virginia 


Quinimont 


0.76 


18.65 


79.26 


I. II 


O.23 


' ' 


Fire Creek 


0.61 


22.34 


75-02 


I.47 


0.56 


E. Kentucky 


Peach Orchard 


4.60 


35-70 


53-28 


6 42 


1.08 




Pike County 


1. So 


26.80 


67.60 


3.80 


0.97 


Alabama 


Cahaba 


1.66 


33-28 


63.04 


2.02 


o.53 


" 


Pratt Co.'s 


1.47 


32.29 


59 50 


6-73 


1.22 


Ohio 


Hocking Valley 


6-59 


35-77 


49-64 


8.00 


1-59 


" 


Muskingum " 


3-47 


37-88 


53-30 


5-35 


2.24 


Indiana 


Block 


8.50 


31.00 


57-50 


3.00 




' ' 




2.50 


44-75 


51-25 


1.50 




W. Kentucky 


Nolin River 


4.70 


33-24 


54-94 


11.70 


2-54 


1 ' 


Ohio County 


3-70 


30.70 


45.oo 


3.16 


I.24 


Illinois 


Big Muddy 


6.40 


30.60 


54.6o 


8.30 


I.50 


' ' 


Wilmington 


15.50 


32.80 


39-90 


11.80 




" 


' ' screenings 


14.00 28.00 


34.20 


23.80 






Duquoin 


8.90 I 23.50 


60.60 


7.00 





The process of combustion consists in the anion of 
the carbon and hydrogen of the fuel with the oxygen 



COMBUSTION — WATER STEAM 93 

of the air. Each atom of carbon combines with two 
atoms of oxygen, and the energetic vibration set up by 
their combination is heat. Bituminous coal contains a 
large percentage of volatile matter which is released 
and flashes into flame when the coal is thrown into the 
furnace, and unless air is supplied in large amounts at 
this stage of the combustion there will be an excess of 
smoke and consequent loss of carbon. On the other 
hand there is a loss in admitting too much air because 
the surplus is heated to the temperature of the furnace 
without aiding the combustion and will carry off to 
the chimney just as many heat units as were required 
to raise it from the temperature at which it entered 
the furnace to that at which it enters the uptake. It 
will therefore be seen that a great advantage will be 
gained by first allowing the air that is needed above 
the fire to pass over or through heated bridge walls or 
side walls. Some kinds of coal need more air for 
their combustion than do others, and good judgment 
and close observation are needed on the part of the 
fireman to properly regulate the supply. 

Some boilers will make steam more economically by 
partly closing the ash-pit doors, while others require 
the same doors to be kept wide open. The quantity 
of air required for the combustion of one pound of 
coal is, by volume, about 150 cu. ft.; by weight, about 
12 lbs. 

The temperature of the furnace is usually about 
2500 , in some cases reaching as high as 3000 . The 
temperature of the escaping gases should not be much 
above nor below 400 F. for bituminous coal. The 
waste heat in the escaping gases can be utilized to 
great advantage by passing them through what are 
called economizers before they escape into the chim- 



94 



ENGINEERING 



ney. These economizers consist of coils or stacks of 
cast iron pipe placed within the flue or breeching lead- 
ing from the boilers to the chimney and are enveloped 
in the hot gases, while the feed water is passed 
through the pipes on its way to the boilers, the result 
being that considerable heat is thus imparted to the 
feed water that would otherwise go to waste. 

In order to attain the highest economy in the burn- 
ing of coal in boiler furnaces two factors are indispen- 




GREEN S FUEL ECONOMIZER UNDER CONSTRUCTION. 



sable, viz., a constant high furnace temperature and 
quick combustion, and these factors can only be 
secured by supplying the fresh coal constantly just as 
fast as it is burned, and also by preventing as much as 
possible the admission of cold air to the furnace. 
This is why the automatic or mechanical stoker, if it 
be of the proper design, is more economical and 
causes less smoke than ,hand firing. The fireman 
when he puts in a fire is prone to shovel in a good 
supply all at once, and this has the tendency to 



COMBUSTION — WATER — STEAM 95 

greatly reduce the temperature of the furnace, while 
at the same time it retards combustion. On the other 
hand the mechanical stoker supplies the coal continu- 
ously only as fast as it is required and no faster, and 
the furnace doors do not need to be opened at all, by 
which a large volume of cold air is prevented from 
entering the furnace and reducing the temperature. 
The author does not wish to be understood as recom- 
mending the adoption and use of mechanical stokers 
to replace hand firing, but he draws this contrast 
between the two methods of firing in order that it 
may be of some benefit to the thousands of honest 
toilers who earn a livelihood by shoveling coal into 
boiler furnaces. 

The problem of the economical use of coal and the 
abatement of the smoke nuisance, especially in our 
large cities, has of late years become so serious that it 
is to the interest of every engineer, and especially 
every fireman, to use the utmost diligence, care and 
good judgment in the use of coal, and to emulate as 
much as possible the methods of the mechanical 
stoker. 

Heat. All matter, whether solid, liquid or gaseous, 
consists of molecules or. atoms, which are in a state of 
continual vibration, and the result of .this vibration is 
heat. The intensity of the heat evolved depends upon 
the degree of agitation to which the molecules are 
subject. 

Until as late as the beginning of the nineteenth 
century two rival theories in regard to the nature of 
heat had been advocated by scientists. The older of 
these theories was that heat was a material substance, 
a subtle elastic fluid termed caloric, and that this fluid 
penetrated matter something like water penetrates a 



ENGINEERING 



sponge. But this theory was shown to be false by the 
wonderful researches and experiments of Count Rum- 
ford at Munich, Bavaria, in 1798. 

By means of the friction between two heavy metallic 
bodies placed in a wooden trough filled with water, 
one of the pieces of metal being rotated by machinery 
driven by horses, Count Rumford succeeded in raising 
the temperature of the water in two and one-half 
hours from its original temperature, of 6o° to 212 F., 
the boiling point, thus demonstrating that heat is not 
a material substance, but that it is due to vibration or 
motion, an internal commotion among the molecules 
of matter. This theory, known as the Kinetic theory 
of heat, has since been generally accepted, although it 
was nearly fifty years after Rumford advocated it in a 
paper read before the Royal Society of Great Britain 
in 1798, before scientists generally became converted 
to this idea of the nature of heat and the science of 
Thermo Dynamics placed on a firm basis. 

During the period from 1840 to 1849 Dr. Joule made 
a series of experiments which not only confirmed the 
truth of Count Rumford's theory that heat was not a 
material substance but a form of energy which may be 
applied to or taken away from bodies, but Joule's 
experiments also established a method of estimating 
in mechanical units or foot pounds the amount of that 
energy. This latter was a most important discovery 
because by means of it the exact relation between heat 
and work can be accurately measured. 

The first law of thermo dynamics is this: Heat and 
mechanical energy or work are mutually convertible. 
That is, a certain amount of work will produce a 
certain amount of heat, and the heat thus produced is 
capable of producing by its disappearance a fixed 



COMBUSTION — WATER — STEAM 



07 



amount of mechanical energy if rightly applied. The 
mechanical energy in the form of heat which, through 
the medium of the steam engine, has revolutionized 
the world, was first stored up by the sun's heat 
millions of years ago in the coal which in turn, by 





^feTy^rr/ti 



P ~fiadd.te$ 



FIGURE 11 



1^ 



combustion, is made to release it for purposes of 
mechanical work. 

The general principles of Dr. Joule's device for 
measuring the amount of work in heat are illustrated 
in Fig. ii. It consisted of a small copper cylinder 



98 ENGINEERING 

containing a known quantity of water at a known 
temperature. Inside the cylinder and extending 
through the top was a vertical shaft to which were 
fixed paddles for stirring the water. Stationary vanes 
were also placed inside the cylinder. Motion was 
imparted to the shaft through the medium of a cord 
or small rope coiled around a drum near the top of the 
shaft and running over a grooved pulley or sheave. 
To the free end of the cord a known weight was 
attached. This weight was allowed to fall through a 
certain distance, and in falling it turned the shaft 
with its paddles, which in turn agitated the water, 
thus producing a certain amount of heat. To illus- 
trate, suppose the weight to be 77.8 lbs., and that by 
means of the crank at the top end of the shaft it has 
been raised to the zero mark at the top of the scale. 
(See Fig. 11.) One pound of water at 39. i° F. is 
poured into the copper cylinder, which is then closed 
and the weight released. At the moment the weight 
passes the 10 ft. mark on the scale, the thermometer 
attached to the cylinder will indicate that the temper- 
ature of the water has been raised one degree. Then 
multiplying the number of pounds in the weight by 
the distance in feet through which it fell will give the 
number of foot pounds of work done. Thus, 
77.8 lbs. x 10 ft. = 778 foot pounds. 

The heat unit or British thermal unit (B. T. U.) is 
the quantity of heat required to raise the temperature 
of one pound of water one degree, or from 39 to 
40 F., and the amount of mechanical work required 
to produce a unit of heat is 778 foot pounds. There- 
fore the mechanical equivalent of heat is the energy 
required to raise 778 lbs. one foot high, or 77.8 lbs. 
10 ft. high, or 1 lb. 778 feet high. Or again, suppose 



COMBUSTION — WATER — STEAM 99 

a one-pound weight falls through a space of 778 ft. or 
a weight of 778 lbs. falls one foot, enough mechanical 
energy would thus be developed to raise a pound of 
water one degree in temperature, provided all the 
energy so developed could be utilized in churning or 
stirring the water, as in Joule's machine. Hence the 
mechanical equivalent of heat is 778 foot pounds. 

Specific Heat. The specific heat of any substance is 
the ratio of the quantity of heat required to raise a 
given weight of that substance one degree in temper- 
ature to the quantity of heat required to raise an equal 
weight of water one degree in temperature when the 
water is at its maximum density, 39. i° F. To illus- 
trate, take the specific heat of lead, for instance, which 
is .031, while the specific heat of water is 1. That 
means that it would require 31 times as much heat to 
raise one pound of water one degree in temperature as 
it would to raise the temperature of a pound of lead 
one degree. 

The following table gives the specific heat of differ- 
ent substances in which engineers are most generally 

interested. 

TABLE 3. 

Water at 39. i° F 1.000 

Ice at 32 F 504 

Steam at 212 F 480 

Mercury 033 

Cast iron 130 

Wrought iron 113 

Soft steel 116 

Copper 095 

Lead 03 1 

Coal 240 

Air 238 

Hydrogen 3.404 

Oxygen 218 

Nitrogen 244 

Sensible Heat and Latent Heat. The plainest and 
most simple definition of these two terms is that given 

L. OF C. 



100 ENGINEERING 

by Sir Wm. Thomson. He says: "Heat given to a 
body and warming it is sensible heat. Heat given to 
a body and not warming it is latent heat." Sensible 
heat in a substance is the heat that can be measured in 
degrees of a thermometer, while latent heat is the heat 
in any substance that is not shown by the ther- 
mometer. 

To illustrate this more fully a brief reference to 
some experiments made by Professor Black in 1762 
will no doubt make the matter plain. It will be 
remembered that at that early date comparatively 
little was known of the true nature of heat, hence Pro- 
fessor Black's investigations and discoveries along this 
line appear all the more wonderful. He procured 
equal weights of ice at 32 F. and water at the same 
temperature, that is, just at the freezing point, and 
placing them in separate glass vessels suspended the 
vessels in a room in which the uniform temperature 
was 47 F. He noticed that in one-half hour the 
water had increased 7 F. in temperature, but that 
twenty half hours elapsed before all of the ice was 
melted. Therefore he reasoned that twenty times 
more heat had entered the ice than had entered the 
water, because at the end of the twenty half hours 
when the ice was all melted the water in both vessels 
was of the same temperature. The water having 
absorbed J° of heat during the first half hour must 
have continued to absorb heat at the same rate during 
the whole of the twenty half hours, although the ther- 
mometer did not indicate it. From this he calculated 
that 7 x 20 = 140 of heat had become latent or hidden 
in the water. 

In another experiment Professor Black placed a 
lump of melting ice, which he estimated to be at a 



COMBUSTION — WATER — STEAM 101 

temperature of 33 F. on the surface, in a vessel con- 
taining the same weight of water at 176 F., and he 
observed that when the whole of the ice had been 
melted the temperature of the water was 33 F., thus 
proving that 143 of heat (i76°-33°) had been 
absorbed in melting the ice and was at that moment 
latent in the water By these two experiments Pro- 
fessor Black established the theory of the latent heat 
of water, and his estimate was very near the truth 
because the results obtained since that time by the 
greatest experimenters show that the latent heat of 
water is 142 heat units, or B. T. U. 

Black's experiment for ascertaining the latent heat 
in steam at atmospheric pressure was made in the 
following simple manner: He placed a flat, open tin 
dish on a hot plate over a fire and into the dish he put 
a small quantity of water at 50 F. In four minutes 
the water began to boil, and in twenty minutes more 
it had all evaporated. In the first four minutes the 
temperature had increased 212 - 50 = 162 , and the 
temperature remained at 212 throughout the twenty 
minutes that it required to evaporate all the water, 
despite the fact that the water had been receiving heat 
during this period at the same rate as during the. first 
four minutes. He therefore reasoned that in the 
twenty minutes the water had absorbed five times as 
much heat as it had in the four minutes, or 162 x 
5 = 810°, without any sensible rise in temperature. 
Therefore the 8io° became latent in the steam. Owing 
to the crude nature of the experiment Professor 
Black's estimate of the number of degrees of latent 
heat in steam was incorrect, as it has been proven by 
many famous experimenters since then that the latent 
heat of steam at atmospheric pressure is 965.7 B. T. U. 



102 ENGINEERING 

It will thus be perceived that what is meant by the 
term latent heat is that quantity of heat which 
becomes hidden or latent when the state of a body is 
changed from a solid to a liquid, as in the case of 
melting ice, or from a liquid to a gaseous state, as 
with water evaporated into steam. But the heat so 
disappearing has not been lost, on the contrary it has, 
while becoming latent, been doing an immense amount 
of work, as can easily be ascertained by means of a 
few simple figures. It has been seen that a heat unit 
is the quantity of heat required to raise one pound of 
water one degree in temperature and also that the 
mechanical equivalent of heat, or, in other words, the 
mechanical energy stored in one heat unit is equal to 
778 foot pounds of work. 

A horse power equals 33,000 ft. lbs. of energy in 
one minute of time, and a heat unit = 778 -*- 33,000 = 
.0236, or about -£$ of a horse power. The work done 
by the heat which becomes latent in converting one 
pound of ice at $2° F. into water at the same temper- 
ature = 142 heat units x 778 ft. lbs. = 110,476 ft. 
lbs., which divided by 33,000 equals 3.34 horse 
power. Again, by the evaporation of one pound 
of water from 32 F. into steam at atmospheric 
pressure, 965.7 units of heat become latent in the 
steam and the work done = 965.7 x 778 = 751,314 ft. 
lbs. = 22.7 horse power. It will thus be seen what 
tremendous energy lies stored in one pound of coal, 
which contains from 12,000 to 14,500 heat units, pro- 
vided all the heat could be utilized in an engine. 

Total Heat of Evaporation. In order to raise the tem- 
perature of one pound of water from the freezing 
point, 32 F., to the boiling point, 212 F., there must 
be added to the temperature of the water 212 — 32 = 



COMBUSTION WATER — STEAM 103 

i8o°. This represents the sensible heat Then to 
make the water boil at atmospheric pressure, or, in 
other words, to evaporate it, there must still be added 
965.7 B. T. U., thus 180 + 965.7= 1,145.7, or in round 
numbers 1,146 heat units. This represents what is 
termed the total heat of evaporation at atmospheric 
pressure and is the sum of the sensible and latent heat 
in steam at that pressure. But if a thermometer were 
held in steam evaporating into the open air, as, for 
instance, in front of the spout of a tea-kettle, it would 
indicate but 212 F. 

When steam is generated at a higher pressure than 
212 , the sensible heat increases and the latent heat 
decreases slowly, while at the same time the total heat 
of evaporation slowly increases as the pressure 
increases, but not in the same ratio. As, for instance, 
the total heat in steam at atmospheric pressure is 
1,146 B. T. U. , while the total heat in steam at 100 lbs. 
gauge pressure is 1,185 B. T. U., and the sensible tem- 
perature of steam at atmospheric pressure is 212 , 
while at 100 lbs. gauge pressure the temperature is 338 
and the latent heat is 876 B. T. U. See table. 

Water. The elements that enter into the composi- 
tion of pure water are the two gases, hydrogen and 
oxygen, in the following proportions: 

By volume, hydrogen 2, oxygen I. 
By weight, 11.1, " 88.9. 

Perfectly pure water is not attainable, neither is it 
desirable nor necessary to the welfare of the human 
race, because the presence of certain proportions of air 
and ammonia add greatly to its value as an agent for 
manufacturing purposes and for generating steam. 
The nearest approach to pure water is rain water, but 
even this contains 2.5 volumes of air to each 100 vol- 



104 ENGINEERING 

umes of water. Pure distilled water, such for instance 
as the return water from steam heating systems, is not 
desirable for use alone in a boiler as it will cause cor- 
rosion and pitting of the sheets, but if it is mixed with 
other water before going into the boiler its use is 
highly beneficial, as it will prevent to a certain degree 
the formation of scale and incrustation. Nearly all 
water used for the generation of steam in boilers con- 
tains more or less scale-forming matter, such as the 
carbonates of lime and magnesia, the sulphates of lime 
and magnesia, oxide of iron, silica and organic matter, 
which latter tends to cause foaming in boilers. 

The carbonates of lime and magnesia are the chief 
causes of incrustation. The sulphate of lime forms a 
hard crystalline scale which is extremely difficult to 
remove when once formed on the sheets and tubes of 
boilers. Of late 'years the intelligent application of 
chemistry to the analyzing of feed waters has been of 
great benefit to engineers and steam users, in that it 
has enabled them to properly treat the water with 
solvents either before it is pumped into the boiler, or 
by the introduction into the boiler of certain scale 
preventing compounds made especially for treating 
the particular kind of water used. Where it is neces- 
sary to treat water in this manner great care and 
watchfulness should be exercised by the engineer in 
the selection and use of a boiler compound. 

From ten to forty grains of mineral matter per 
gallon are held in solution by the waters of the differ- 
ent rivers, streams and lakes; well and mine water 
contain still more. 

Water contracts and becomes denser in cooling until 
it reaches a temperature of 39. i° F. , its point of great- 
est density. Below this temperature it expands and 



COMBUSTION WATER STEAM 



105 



at 32 F. it becomes solid or freezes, and in the act of 
freezing it expands considerably, as every engineer 
who has had to deal with frozen water pipes can tes- 
tify. 

Water is 815 times heavier than atmospheric air. 
The weight of a cubic foot of water at 39. i° is approx- 
imately 62.5 lbs., although authorities differ on this 
matter, some of them placing it at 62.379 lbs., and 
others at 62.425 lbs. per cubic foot. As its tempera- 
ture increases its weight per cubic foot decreases until 
at 212 F. one cubic foot weighs 59.76 lbs. 

The table which follows is compiled from various 
sources and gives the weight of a cubic foot of water 
at different temperatures. 

Table 4 



Temper- 


Weight per 


Temper- 


Weight per 


Temper- 


Weight per 


ature 


Cubic Foot 


ature 


Cubic Foot 


ature 


Cubic Foot 


32° F. 


62.42 lbs. 


1 32° F. 


61.52 lbs. 


230° F. 


59-37 lbs. 


42° 


62.42 


142 


61.34 


240° 


59.IO 


52° 


62.40 


152 


61.14 


'250° 


58.85 


62° 


62.36 


162° 


60.94 


260° 


58.52 


72° 


62.30 


172° 


60.73 


270° 


58.21 


82° 


62.21 


182 


60.50 


300° 


57-26 


92° 


62.II 


IQ2° 


60.27 


330° 


56.24 


102° 


62.OO 


202° 


60.02 


360° 


55.16 


112° 


61.86 


212° 


59-76 


3 90° 


54.03 


122° 


61.70 


220° 


59-64 


420 ° 


52.86 



The boiling point of water varies according to the 
pressure to which it is subject. In the open air at sea 
level the boiling point is 212 F. When confined in a 
boiler under steam pressure the boiling point of water 
depends upon the pressure and temperature of the 
steam, as, for instance, at 100 lbs. gauge pressure the 
temperature of the steam is 338 F., to which temper- 



106 ENGINEERING 

ature the water must be raised before its molecules 
will separate and be converted into steam. In the 
absence of any pressure, as in a perfect vacuum, water 
boils at 32 F. temperature. In a vacuum of 28 in., 
corresponding to an absolute pressure of .943 lbs., 
water will boil at ioo°, and in a vacuum of 26 in., at 
which the absolute pressure is 2 lbs., the boiling point 
of water is 127 F. On the tops of high mountains in 
a rarefied atmosphere water will boil at a much lower 
temperature than at sea level, for instance at an 
altitude of 15,000 ft. above sea level water boils at 
184° F. 

Steam. Having discussed to some extent the phys- 
ical properties of water, it is now in order to devote 
some time to the study of the nature of steam, which 
is simply water in its gaseous form made so by the 
application of heat. 

As has been stated in another portion of this book, 
matter consists of molecules or atoms inconceivably 
small in size, yet each having an individuality, and in 
the case of solids or liquids, each having a mutual 
cohesion or attraction for the other, and all being in a 
state of continual vibration more or less violent 
according to the temperature of the body. 

The law of gravitation which holds the universe 
together, also exerts its wonderful influence on these 
atoms and causes them to hold together with more or 
less tenacity according to the nature of the substance. 
Thus it is much more difficult to chip off pieces of iron 
or granite than it is of wood. But in the case of water 
and other liquids the atoms, while they adhere to each 
other to a certain extent, still they are not so hard to 
separate, in fact, they are to some extent repulsive to 
each other, and unless confined within certain bounds 



COMBUSTION — WATER — STEAM 107 

the atoms will gradually scatter and spread out, and 
finally either be evaporated or sink out of sight in the 
earth's surface. Heat applied to any substance tends 
to accelerate the vibrations of the molecules, and if 
enough heat is applied it will reduce the hardest sub- 
stances to a liquid or gaseous state. 

The process of the generation of steam from water 
is simply an increase of the natural vibrations of the 
molecules of the water, caused by the application of 
heat until they lose all attraction for each other and 
become instead entirely repulsive, and unless confined 
will fly off into space. But being confined they con- 
tinually strike against the sides of the containing 
vessel, thus causing the pressure which steam or any 
other gas exerts when under confinement. 

Of course steam, like other gases, when under pres- 
sure is invisible, but the laws governing its action are 
well known. These laws, especially those relating to 
the expansion of steam, will be more fully discussed in 
the chapters on the Indicator. The temperature of 
steam in contact with the water from which it is 
generated, as for instance in the ordinary steam boiler, 
depends upon the pressure under which it is gener- 
ated. Thus at atmospheric pressure its temperature 
is 212° F. If the vessel is closed and the pressure 
increased the temperature of the steam and also that 
of the water rises. 

Saturated Steam. When steam is taken directly from 
the boiler to the engine without being superheated, it 
is termed saturated steam. This does not necessarily 
imply that it is wet and mixed with spray and 
moisture. 

Superheated Steam. When steam is conducted into 
or through a vessel or coils of pipe separate from the 



108 ENGINEERING 

boiler in which it was generated and is there heated to 
a higher temperature than that due to its pressure, it 
is said to be superheated. 

Dry Steam. When steam contains no moisture it is 
said to be dry. Dry steam may be either saturated or 
superheated. 

Wet Steam. When steam contains mist or spray 
intermingled it is termed wet steam, although it may 
have the same temperature as dry saturated steam of 
the same pressure. 

During the further consideration of steam in this 
book, saturated steam will be mainly under discussion 
for the reason that this is the normal condition of 
steam as used most generally in steam engines. 

Total Heat of Steam. The total heat in steam includes 
the heat required to raise the temperature of the water 
from 32 F. to the temperature of the steam plus the 
heat required to evaporate the water at that tempera- 
ture. This latter heat becomes latent in the steam, 
and is therefore called the latent heat of steam. 

The work done by the heat acting within the mass of 
water and causing the molecules to rise to the surface 
is termed by scientists internal work, and the work 
done in compressing the steam already formed in the 
toiler or in pushing it against the superincumbent 
atmosphere, if the vessel be open, is termed external 
work. There are, therefore, in reality three elements 
to be taken into consideration in estimating the total 
heat of steam, but as 'the heat expended in doing 
external work is done within the mass itself it may, for 
practical purposes, be included in the general term 
latent heat of steam. 

De?isity of Steam. The expression density of steam 
means the actual weight in pounds or fractions of a 



COMBUSTION WATER STEAM 109 

pound avoirdupois of a given volume of steam, as one 
cubic foot. This is a very important point for young 
engineers especially to remember, so as not to get the 
two terms, pounds pressure and pounds weight, mixed, 
as some are prone to do. 

Volume of Steam. By this term is meant the volume 
as expressed by the number of cubic feet in one pound 
weight of steam. 

Relative Volume of Steam. This expression has refer- 
ence to the number of volumes of steam produced 
from one volume of water. Thus the steam produced 
by the evaporation of one cubic foot of water from 
39 F. into steam at atmospheric pressure will occupy 
a space of 1646 cu. ft., but, as the steam is compressed 
and the pressure allowed to rise, the relative volume of 
the steam becomes smaller, as for instance at 100 lbs. 
gauge pressure the steam produced from one cubic 
foot of water will occupy but 237.6 cu. ft., and if the 
same steam was compressed to 1,000 lbs. absolute or 
985.3 lbs. gauge pressure it would then occupy only 
30 cu. ft. 

The condition of steam as regards its drvness may 
be approximately estimated by observing its appear- 
ance as it issues from a pet cock or other small open- 
ing into the atmosphere. Dry or nearly dry steam 
containing about 1 per cent, of moisture will be trans- 
parent close to the orifice through which it issues, and 
even if it is of a grayish white color it may be esti- 
mated to contain not over 2 per cent, of moisture. 

Steam in its relation to the engine should be consid- 
ered in the character of a vehicle for transferring the 
energy, created by the heat, from the boiler to the 
engine. For this reason all steam drums, headers and 
pipes should be thoroughly insulated in order to 



110 



ENGINEERING 



prevent, as much as possible, the loss of heat or energy 
by radiation. 

Table 5, showing the properties of saturated steam, 
is compiled mainly from Kent's Steam Boiler Eco?wmy. 
The decimals have not been carried out in the columns 
headed Relative Volume and Weight of 1 cu. ft. of 
steam, as their absence will affect the results very 
little. 



TABLE 5 
Properties of Saturated Steam 









Total 


Heat 






S 





3 


a 




above 


32" F. 


_^ 


g 


2 2 


£j 












Mjc'l 


"p 


£0 




«2 


5 w 


a £ 




> g 


S 


Q 


£ 1 

C I " L ' 


£ '2 

C/3-pi t 3 


►4 


(4 


^3 




29.74 


.089 


32. 


O. 


1091.7 


IO9I.7 


208,080 


3333-3 


.0003 


29.67 




122 


40. 


8 




1094. 1 


IO86. 1 


154,330 


2472.2 


.0004 


29.$6 




176 


50. 


18 




1097.2 


IO79.2 


107,630 


1 724. 1 


.0006 


29.4O 




254 


60. 


28 


01 


I IOO. 2 


IO72.2 


76,370 


1223.4 


.0008 


29.I9 




359 


70. 


38 


02 


1 103. 3 


IO65.3 


54,66o 


875.61 


.0011 


28.9O 




502 


80. 


48 


04 


1106.3 


I058.3 


39,690 


635.80 


.0016 


28.51 




692 


90. 


5S 


06 


1109.4 


I05 I..3 


2Q.290 


469.20 


.0021 


28 OO 




943 


100. 


68 


08 


1112.4 


I044.4 


21,830 


349-70 


.0028 


2y.88 


1 




102. 1 


70 


09 


1113.1 


IO43.O 


20,623 


334-23 


.0030 


25 85 


2 




126.3 


94 


4A 


1120.5 


1026.0 


10,730 


173-23 


.0058 


23.83 


3 




141. 6 


109 


9 


1125.1 


IOI5.3 


7,325 


118.00 


.0085 


21.78 


4 




I53-I 


121 


4 


1128 6 


IOO7.2 


5,588 


89.S0 


.0111 


19-74 


5 




162.3 


130 


7 


1131-4 


IOOO. 7 


4,530 


72.50 


.0137 


17.70 


6 




170. 1 


138 


6 


1133.8 


995-2 


3,8i6 


61.10 


.0163 


15.67 


7 




176.9 


145 


4 


H35-9 


990- 5 


3,302 


53-oo 


.0189 


13.63 


8 




182.9 


151 


5 


1 137- 7 


986.2 


2,912 


46.60 


.0214 


11.60 


9 




188.3 


156 


9 


U39-4 


982.4 


2,607 


41.82 


.0239 


9-56 


10 




193.2 


161 


9 


1 1 40. 9 


979.0 


2,361 


37-So 


.0264 


7.52 


11 




197.8 


166 


5 


1142 3 


975-8 


2,159 


34.61 


.0289 


5-49 


12 




202.0 


170 


7 


H43-5 


972.8 


1,990 


31.90 


.0314 


3-45 


13 




205.9 


174 


7 


1 144. 7 


970.0 


1,846 


29.60 


.0338 


1. 41 


14 




209.6 


178 


4 


1145.9- 


967.4 


1,721 


27-5o 


.0363 


0.00 


M 


7 


212.0 


180 


9 


1 1 46. 6 


965./ 


1,646 


26.36 


.0379 



COMBUSTION WATER— STEAM 



111 



Table 5 — Continued 









Total 


Heat 






2 


c 


31—1 


5 c" 


fc 


Above 


32° F. 


rt co 


1 


2 2 


■ 


P-I •" 




p*S 


m 


S a, 


ffi^"| 


> 


-"C/2 


2 - 




3 °* 


Q 








% 


IS? 

3 • 


u 3 


0-1 


-D.-I 




a * 


a ffi 




' X 


_] 


-J ° 


0.3 


15 


213-3 


181. 9 


1 146. 9 


965.O 


1,614 


25.90 


.O3S7 


I 


3 


16 


216.3 


185.3 


1147.9 


962.7 


1,519 


24-33 


.O4II 


2 


3 


17 


219.4 


188.4 


1148.9 


960.5 


i,434 


23.OO 


•0435 


3 


3 


18 


222.4 


191.4 


1149-8 


958.3 


i,359 


2I.8o 


.0459 


4 


3 


19 


225.2 


194.3 


1150.6 


956.3 


1,292 


20.70 


.0483 


5 


3 


20 


227.9 


197.0 


II5I.5 


954-4 


1,231 


I9.72 


.0507 


6 


3 


21 


230.5 


199.7 


1152.2 


952.6 


1,176 


18.84 


.0531 


7 


3 


22 


233-0 


202.2 


H53-0 


950.8 


1,126 


18.03 


.0555 


8 


3 


23 


235-4 


204.7 


II53.7 


949-1 


1,080 


I7.30 


.0578 


9 


3 


24 


237.8 


207.0 


II54.5 


947-4 


1,038 


16.62 


.0602 


10 


3 


25 


240.0 


209.3 


II55.I 


945-8 


998 


lo.OO 


.062 5 


11 


3 


26 


242.2 


211. 5 


H55.8 


944- 3 


962 


15.42 


.0649 


12 


3 


27 


244-3 


213-7 


1156.4 


942.8 


929 


14.90 


.0672 


13 


3 


28 


246.3 


215-7 


H57-I 


94L3 


898 


I4.4O 


.0696 


14 


3 


29 


248.3 


217.8 


H57-7 


939-9 


869 


I3-9I 


.O7I9 


15 


3 


30 


250.2 


219.7 


1158.3 


938.9 


841 


I3.50 


.0742 


16 


3 


31 


252.1 


221.6 


1158.8 


937-2 


816 


13.07 


.0765 


17 


3 


32 


254.0 


223.5 


II59-4 


935-9 


.792 


12.68 


.0788 


iS 


3 


33 


255.7 


225.3 


"59.9 


9346 


769 


12.32 


.08l2 


19 


3 


34 


257.5 


227.1 


1 160. 5 


933-4 


748 


12.00 


.O835 


20 


3 


3^ 


259.2 


228.8 


1161.0 


932.2 


72S 


11.66 


.0858 


21 


3 


36 


260.8 


230.5 


1161.5 


931 


709 


11.36 


.0880 


22 


3 


37 


262.5 


232.1 


1162.0 


929. S 


691 


11.07 


.0903 


23 


3 


38 


264.0 


233.8 


1 162. 5 


92S.7 


674 


10.80 


.0926 


24 


3 


39 


265.6 


235.4 


1162.9 


927.6 


658 


10.53 


.0949 


25 


• 3 


40 


267.1 


236.9 


1163.4 


926.5 


642 


10.28 


.0972 


26 


3 


4i 


268.6 


238.5 


1163.9 


925.4 


627 


10.05 


•0995 


27 


3 


42 


270.1 


240.0 


1164-3 


924.4 


613 


9-83 


.IOI8 


28 


3 


43 


27L5 


241-4 


1 164. 7 


923 3 


600 


9.61 


.1040 


29 


3 


44 


272.9 


242.9 


1165.2 


922.3 


587 


9.41 


• IO63 


30 


3 


45 


274.3 


244-3 


1165.6 


921.3 


575 


9.21 


.IO86 


3i 


• 3 


46 


275-7 


245-7 


1 166.0 


920.4 


563 


9.02 


.IIO8 


32 


3 


47 


277.0 


247.0 


1 166. 4 


919.4 


552 


8.84 


. 1 1.3 I 


33 


3 


48 


278.3 


248.4 


1166.8 


918.5 


54i 


8.67 


■1153 


34 


• 3 


49 


279.6 


249.7 


1167.2 


917.5 


53i 


8.50 


.II76 


35 


■3 


5o 


280.9 


251.0 


1167.6 


916.6 


520 


8-34 


.II98 


36 


■3 


5i 


282.1 


252.2 


1168.0 


915.7 


5ii 


8.19 


.1221 


37 


•3 


52 


283.3 


253-5 


1168.4 


914.9 


502 


8.04 


•1243 



112 



ENGINEERING 









Table 5 — Continued 








<u 




Total Heat 






a 





£c 


g d 




above 


32° F. 


^ 


E 


c £ 




[In m 




4) <U 


II 








> 


1° 


, Xj 


vw 

P* £ 


rt •- 


1 5 


1^ 


<u ft 

to . 


s* 


H g 1 


*c? 


"V ? 


fe^ rt 


»3 


■~B 


M 0) 


03X1 


S-O 


Q 


| | 


5 ° 


3 = 


P4 


h 


0^ 




< 




c S- 


a **" 








5° 


33-3 


53 


284.5 


254-7 


1168.7 


9I4-0 


492 


1 - 
7.90 


1266 


39-3 


54 


285.7 


256.0 


1 [65. 1 


9I3.I 


.484 


7-76 


1288 


40.3 


55 


286.9 


257.2 


1169 4 


912.3 


476 


7-63 


1311 


4i-3 


56 


288.1 


258.3 


1 169. 8 


9H-5 


468 


7- 50 


1333 


42.3 


57 


289.I 


259-5 


1 1 70. 1 


910.6 


460 


7.38 


1355 


43 3 


58 


29O.3 


260.7 


1170.5 


909.8 


453 


7.26 


1377 


44-3 


59 


291.4 


261.8 


1 170.8 


909.0 


44<J 


7-14 


1400 


45-3 


60 


292.5 


262.9 


1171.2 


908.2 


439 


7-03 


1422 


46.3 


61 


293.6 


264.0 


II7I.5 


Q07-5 


432 


6.92 


1444 


47-3 


62 


294.7 


265.1 


1171.8 


906.7 


425 


6.82 


1466 


483 


63 


295-7 


266.2 


1172.1 


905-9 


419 


6. 72 


1488 


49-3 


64 


296.8 


267.2 


1172.4 


905.2 


413 


6.62 


1511 


50.3 


65 


297.8 


268.3 


1172.8 


9045 


407 


6-53 


1533 


5i.3 


66 


298.8 


269.3 


H73-I 


903-7 


401 


6 43 


1555 


52.3 


67 


299.8 


270.4 


H73-4 


903.0 


395 


6-34 


1577 


53 3 


68 


300.8 


271 4 


H73-7 


902.3 


390 


6.25 


1599 


54-3 


69 


301.8 


272.4 


1174-0 


901.6 


384 


6.17 


1621 


55-3 


~o 


302.7 


273-4 


H74-3 


900.9 


379 


6.09 


1643 


56.3 


7i 


3037 


274.4 


H74-6 


900.2 


374 


6.01 


1665 


57-3 


72 


304.6 


275.3 


H74-8 


899-5 


369 


5-93 


1687 


53.3 


73 


305-6 


276.3 


H75-I 


89S.9 


305 


5.85 


1709 


59-3 


74 


306.5 


277.2 


1175.4 


898.2 


360 


5.78 


1731 


60.3 


75 


307-4 


278.2 


H75-7 


897-5 


356 


5.71 


1753 


61.3 


76 


308.3 


279.1 


1176.0 


896.9 


35i 


5.63 


1775 


62.3 


77 


309.2 


280.0 


1176.2 


896.2 


347 


5-57 


1797 


63-3 


78 


310. 1 


280.9 


1176.=; 


895.6 


343 


5.50 


1819 


64.3 


79 


310.9 


281.8 


1176.8 


895.0 


339 


5-43 


1840 


65 3 


80 


311. 8 


2827 


1177.0 


894-3 


334 


5-37 


1862 


66.3 


81 


312.7 


283.6 


II77-3 


893-7 


33i 


5-31 


1884 


67.3 


' 82 


313-5 


284.5 


11*77.6 


893.1 


327 


5-25 


1906 


68.3 


83 


3144 


285 = 3 


1177.S 


892.5 


323 


5.18 


1928 


69-3 


84 


315-2 


286.2 


1178.1 


891.9 


320 


5-13 


1950 


70 3 


35 


316.0 


287.0 


1178.3 


891.3 


316 


5.07 


1971 


71.3 


86 


316.8 


287.9 


IT 78.6 


890.7 


313 


5.02 


1993 


72.3 


87 


317.7 


288.7 


it 78. 8 


890.1 


309 


4.96 


2015 


73-3 


88 


318.5 


289. 5 


1179.1 


889.5 


306 


4.91 


2036 


74-3 


89 


3190 


2904 


1179.3 


8S8.9 


303 


4.86 


2058 


75-3 


90 


320.0 


291.2 


1179.6 


888.4 


299 


4.81 


2080 



COMBUSTION WATER STEAM 



113 











Table 5 — Continued 










(0 




Total 


Heat 






E 





3~ 


3 C 




above 


32° F. 


ca tn 


E 


.5 " 


. 

(jr. m 


en 6" 


£ 6* 

0h OT 


d« 


« a 


E m 


5^1 


> 






<u ft 

03 X! 


3 a 


Q 




1 = 


-4-> <D 

3 a 


"3 


3 x 
U 3 


*: 


76.3 


91 


320.8 


292.0 


1179.8 


887.8 


296 


4.76 


.2102 


77 


3 


92 


321.6 


292.8 


1180.0 


887.2 


293 


4 


7i 


• 2123 


78 


3 


93 


322.4 


293.6 


1180.3 


886.7 


290 


4 


66 


■2145 


79 


3 


94 


323.1 


294.4 


1180.5 


886 1 


287 


4 


62 


.2166 


So 


3 


95 


3239 


295.1 


1180 7 


885.6 


285 


4 


57 


.2188 


81 


3 


96 


324.6 


295-9 


1181.0 


885.0 


282 


4 


53 


.2210 


82 


3 


97 


325.4 


296.7 


1181.2 


884.5 


279 


4 


48 


.2231 


S3 


3 


98 


326.1 


297.4 


1181.4 


884.0 


276 


4 


44 


•2253 


84 


3 


99 


326.8 


298.2 


1181.6 


883.4 


274 


4 


40 


.2274 


85 


3 


100 


3276 


298.9 


1181.8 


882.9 


271 


4 


36 


.2296 


86 


3 


101 


328.3 


299.7 


1182.1 


882.4 


268 


4 


32 


.2317 


87 


3 


102 


329.0 


300.4 


1182.3 


881.9 


266 


4 


28 


.2339 


S3 


:■ 


103 


32Q.7 


301. 1 


1182.5 


881.4 


264 


4 


24 


.2360 


89 


3 


104 


330.4 


301.9 


1182 7 


880.8 


261 


4 


20 


.2382 


90 


3 


105 


331 1 


302.6 


1182.9 


880.3 


259 


4 


16 


.2403 


9i 


3 


106 


331.8 


303.3 


1183.1 


879.8 


257 


4 


12 


■2425 


92 


3 


107 


332.5 


304.0 


1183.4 


879.3 


254 


4 


09 


.2446 


93 


3 


108 


333-2 


304.7 


1183.6 


878.8 


252 


4 


05 


.2467 


94 


3 


109 


333-9 


305-4 


1183.8 


878.3 


250 


4 


02 


.2489 


95 


3 


no 


334-5 


306.1 


1184.0 


877.9 


248 


3 


98 


.2510 


96 


3 


in 


335-2 


306.8 


1184.2 


877.4 


246 


3 


95 


.2531 


97 


3 


112 


335-9 


307.5 


11S4.4 


876,9 


244 


3 


92 


•2553 


9 S 


3 


113 


336-5 


308.2 


1184.6 


876.4 


242 


3 


88 


• 2574 


99 


3 


114 


337-2 


308.8 


1184.8 


875.9 


240 


3 


85 


.2596 


100 


3 


115 


337.8 


309-. 


1185.0 


875.5 


238 


3 


82 


.2617 


101 


3 


116 


338.5 


310.2 


1185.2 


875.o 


236 


3 


79 


.2638 


102 


3 


117 


339-1 


310.8 


1185.4 


874.5 


234 


3 


76 


.2660 


103 


3 


1 1.8 


339-7 


311.5 


1185.6 


874.1 


232 


3 


73 


.2681 


104 


3 


119 


3404 


312. 1 


1185.8 


873.6 


230 


3 


70 


.2703 


105 


3 


120 


341.0 


312 8 


1185.9 


873.2 


22S 


3 


67 


.2764 


106 


3 


121 


341.6 


3134 


1 186. 1 


872.7 


227 


3 


64 


• 2745 


107 


3 


122 


342.2 


314. i' 


1186.3 


872.3 


225 


3 


62 


.2766 


108 


3 


123 


342.9 


314-7 


1 186. 5 


871.8 


223 


3 


59 


.2788 


109 


3 


124 


343-5 


315.3 


1186.7 


871.4 


221 


3 


56 


.280Q 


no 


3 


125 


344- 1 


316.0 


1 186.9 


870.9 


220 


3 


53 


.2830 


III 


3 


126 


344-7 


316.6 


1187.1 


870.5 


218 


3 


5i 


2851 


112 


3 


127 


345-3 


317.2 


1187.3 


870.0 


216 


3 


48 


.2872 


113 


3 


128 


345-9 


3I7.S 


1187.4 


869.0 


215 


3 


46 


.2894 



114 



ENGINEERING 











Table $ — Continued 








<u 




Total Heat 






S 





SH 


3 d 




Above 


32° F. 


^ 


a 


c 2 


£j 












M 


"0 
> 






3h J- 


v tn 


B w 


XI .. 


















U a 




;S ft 


t -1 oj 


*J? 


3LJ 


2 


•S 


"^ 


HJS 


3 tn 
rt-Q 


8x> 


Q 


1 £ 

J3 X 


X! rt 


a x 


& 


h 


• O 


"4-3 


129 


346.5 


318.4 


1187.6 


869.2 


213 


3-43 


.2915 


115 


3 


130 


347- 1 


319-1 


1187.8 


868.7 


212 


3-4i 


.2936 


116 


3 


131 


347.6 


319-7 


1188.0 


868.3 


210 


3-38 


.2957 


117 


3 


132 


348.2 


320.3 


1188.2 


867.9 


209 


3-36 


.2978 


ti6 


3 


133 


348.8 


320.8 


1188.3 


867.5 


207 


3-33 


.3000 


119 


3 


134 


349-4 


321.5 


1188.5 


867.0 


206 


3.3i 


.3021 


120 


3 


i35 


350.0 


322.1 


1188.7 


866.6 


204 


3-29 


.3042 


121 


3 


136 


350.5 


322.6 


1188.9 


866.2 


203 


3-27 


.3063 


1 22 


3 


137 


35r. 1 


323.2 


1189.0 


865.8 


201 


3-24 


.3084 


123 


3 


138 


351-8 


323.8 


1189.2 


865.4 


200 


3.22 


.3I05 


124 


3 


139 


352.2 


324.4 


1 189.4 


865.0 


199 


3.20 


.3126 


125 


3 


140 


352.8 


325.0 


1189.5 


864.6 


197 


3-i8 


.3147 


126 


3 


141 


353-3 


325-5 


1189.7 


864.2 


196 


3.16 


.3169 


127 


3 


142 


353-9 


326.1 


1189.9 


863.8 


195 


3.14 


.3190 


I 28 


3 


H3 


354-4 


326.7 


1 190.0 


863.4 


193 


3-" 


.3211 


129 


3 


144 


355.o 


327.2 


1190.2 


863.0. 


192 


3-09 


.3232 


130 


3 


i45 


355.5 


327.8 


1 190 4 


862.6 


191 


3-07 


•3253 


131 


3 


146 


356.o 


328.4 


1 1 90. 5 


862.2 


190 


3-05 


.3274 


133 


3 


148 


357-1 


329.5 


1 190.9 


861.4 


187 


3.02 


.3316 


135 


3 


150 


358.2 


330.6 


T191.2 


860.6 


1S5 


2.98 


.3358 


140 


3 


155 


360.7 


333-2 


1192.0 


858.7 


179 


2.89 


.3463 


MS 


3 


160 


363.3 


335-9 


1192.7 


856.9 


174 


2. So 


.3567 


150 


3 


165 


365.7 


338.4 


"93 5 


855.1 


169 


2.72 


•3671 


155 


3 


170 


36S.2 


340.9 


1 194. 2 


853-3 


164 


2.65 


•3775 


160 


3 


175 


370.5 


343-4 


1194.9 


851.6 


160 


2.58. 


.3879 


165 


3 


180 


372.8 


345-8 


"95-7 


849.9 


156 


2.51 


•3983 


170 


3 


185 


375-1 


348.1 


1196,3 


848.2 


152 


2-45 


.4087 


175 


3 


190 


377-3 


35o.4 


1197.0 


846.6 


148 


2-39 


.4191 


1 So 


3 


i95 


379-5 


352.7 


1197.7 


845.0 


144 


2-33 


.4296 


[85 


3 


200 


381.6 


354-9 


1198.3' 


843.4 


141 


2.27 


.4400 


[90 


3 


205 


383-7 


357-1 


1 199.0 


841.9 


138 


2.22 


.4503 


195 


3 


210 


385-7 


359-2 


1199.6 


840.4 


135 


2.17 


.4605 


200 


3 


215 


387 7 


361.3 


1200.2 


838.9 


132 


2.12 


.4707 


2" 5 


3 


220 


389-7 


362.2 


1 200. 8 


838.6 


129 


2.06 


.4852 


245 


3 


260 


404.4 


377-4 


1205.3 


827.9 


no 


1.76 


.5686 


285 


3 


300 


417.4 


390.9 


1209.2 


818.3 


96 


i-53 


.6515 


485 


3 


500 


467.4 


443- 5 


1224.5 


781.0 


59 


•94 


1.062 


685 


3 


700 


504.1 


482.4 


1235.7 


753-3 


42 


.68 


I.470 


9853 


1000 


546.8 


528.3 


1248.7 


720.3 


30 


.48 


2.082 



COMBUSTION — WATER — STEAM 115 



Questions 

1. What is combustion? 

2. What is one of the main factors in combustion? 

3. Of what is air composed? 

4. In what proportion are these two gases combined? 

5. What is the principal constituent of coal and 
other fuels? 

6. What other valuable constituent is contained in 
bituminous coal? 

7. What is the usual temperature of a boiler furnace 
when in active operation? 

8. About what should be the temperature of the 
escaping gases? 

9. W T hat two factors are indispensable in the eco- 
nomical use of coal? 

10. What is heat? 

11. What is the heat unit? 

12. What is the mechanical equivalent of heat? 

13. How many heat units are there in one pound of 
carbon? 

14. How many heat units are there in one pound of 
hydrogen gas? 

15. What is specific heat? 

16. What is sensible heat? 

17. What is latent heat? 

18. Is the latent heat imparted to a body lost? 

19. What is meant by the total heat of evaporation? 

20. How much heat expressed in heat units is 
required to evaporate one pound of water from a tem- 
perature of 32 into steam at atmospheric pressure? 

21. Name the two elements composing pure water. 

22. In what proportion are these two gases combined 
in the formation of water? 



116 ENGINEERING 

23. Is perfectly pure water desirable for use in steam 
boilers? 

24. What causes scale to form in boilers? 

25. What proportion of mineral matter is usually 
found in water? 

26. What is steam? 

27. Of what does matter consist? 

28. How does the application of heat to any sub- 
stance affect its molecules? 

29. In what particular manner does heat affect the 
molecules of water? 

30. Is steam under pressure visible? 

31. What is saturated steam? 

32. What is dry steam? 

33. What is superheated steam? 

34. What is meant by the term total heat in steam? 

35. What is meant by the density of steam? 

36. What is meant by the volume of steam? 

37. What is the weight of a cubic foot of water at 
39. 1 ° temperature? 

38. What is the weight of a cubic foot of water at a 
temperature of 212 ? 

39. What is the boiling point of water in the open 
air at sea level? 

40. At what temperature will water boil in a perfect 
vacuum? 

41. What is meant by the relative volume of steam? 



CHAPTER V 

EVAPORATION TESTS 

Evaporation tests, object of — Preparing for a test — Suggestions as 
to apparatus needed — Taking the temperature of the feed 
water — Precautions necessary to obtain accurate results — 
Duration of test — Feeding a boiler during a test — How to pro- 
ceed if the boiler is fed by an injector — Determining the per- 
centage of moisture in the steam — Moisture in the coal — 
Chimney draft — Draft gauge — Rules for determining the 
results of a test — "Equivalent evaporation," how to com- 
pute — Factors of evaporation — Boiler horse power. 

Evaporation Tests. The object of making evapora- 
tion tests of steam boilers is primarily to ascertain how 
many pounds of water the boilers are evaporating per 
pound of coal burned; but these tests can and should 
be made to determine several other important points 
with reference to the operation of the boilers, as for 
instance: I. The efficiency of the boiler and furnace 
as an apparatus for the consumption of fuel and the 
evaporation of water; whether this apparatus is per- 
forming its guaranteed duty in this respect, and how it 
compares with a known standard. 2. To determine 
the relative economy of different varieties of coal, also 
to determine the relative value of fuels other than 
coal, such as oil, gas, etc. 3. To ascertain whether or 
not the boilers as they are operated under ordinary 
every day conditions are being run as economically as 
they should be. 4. In case the boilers, owing to an 
increased demand for steam, fail to supply a sufficient 
quantity without forcing the fires, whether or not addi- 
tional boilers are needed, or whether the trouble could 
117 



118 ENGINEERING 

be overcome by a change of conditions in operating 
them. 

As was stated in the chapter oh boiler setting, every 
steam plant can and should be equipped with the 
necessary apparatus for making evaporation tests, and 
every engineer should take pride in making a good 
showing in the economical use of coal, and, be it said 
to their credit, the majority of engineers do this, 
although many of them are working under conditions 
that prevent them from doing all that they might 
desire along this line. Too many engineers are com- 
pelled to look after work entirely outside of and 
foreign to their vocation as engineers, often having to 
go to some distant part of the building to make repairs 
to some part of the machinery, leaving their boiler and 
engine to care for themselves for the time being, thus 
not only endangering the safety of property, but of 
life as well. But conditions are gradually changing 
for the better in this respect, and employers and own- 
ers of steam plants are coming more and more to rec- 
ognize the fact that the engineer is something more 
than a mere handy man about a factory, in fact, that 
he has a distinct and responsible vocation to be ful- 
filled, viz., the safe and economical operation of the 
plant where the power comes from. 

The author proposes to present in as brief a manner 
as possible a few simple suggestions and rules for the 
benefit of engineers who desire to make evaporation 
tests with a view of determining one or more of the 
points mentioned at the beginning of this chapter. 

Tests for the last three purposes named can be made 
by the regular engineering force of the plant, but in 
case a controversy should arise between the maker of 
the boiler and the purchaser regarding the first men- 



EVAPORATION TESTS 119 

tioned point, viz., the guaranteed efficiency of the 
boiler or the furnace, the services of experts in boiler 
testing may be resorted to. 

Preparing for a Test. All testing apparatus should be 
kept in such shape that it will not take three or four 
days to get it ready for making a test. On the con- 
trary, it can be and should be always kept in condition 
ready for use, so that the preparations for making a 
test will occupy but a short time. A small platform 
scale sufficiently large for weighing a wheel-barrow 
load of coal should also be provided in addition to the 
apparatus referred to in Chapter II. 

The capacity of each of the two tanks therein men- 
tioned, and which are illustrated in Fig. 10, can be 
determined in two ways, either by measuring the 
cubical contents of each or by placing them one at a 
time on the scales, filling them with water to within a 
few inches of the top, and note the weight. Also make 
a permanent mark on the inside at the water level. 
The water should then be permitted to run out until 
within an inch or so of the outlet pipe near the bottom, 
where another plain mark should be made, after which 
the empty tank should be again weighed, then by sub- 
tracting the last weight from the first the exact number 
of pounds of water that the tank will contain between 
the top and bottom marks can be determined and a 
note made of it. 

It is much more convenient to have each tank con- 
tain the same quantity of water, although not abso- 
lutely necessary. The tanks should also be numbered 
I and 2 respectively in order to prevent confusion in 
keeping a record of the number of tanks full of water 
used during the test. Care should be exercised to 
have the water with which the tanks are filled while on 



120 ENGINEERING 

the scale, at or near the same temperature as that at 
which it is to be fed into the boiler during the test. 
Otherwise there is liability of error owing to the varia- 
tion in the weight of water at different temperatures. 
In order to guard against this, the capacity in cubic 
feet of each tank between the top and bottom marks 
should be ascertained by measuring the distance 
between the marks, also the diameter, or, if the tanks 
be square, the length of one side, after which the 
cubical contents can be easily figured and noted down. 
By knowing the capacity in cubic feet of each tank all 
possibility of error in the weight of feed water will be 
eliminated. 

The scales for weighing the coal can be fitted with a 
temporary wooden platform large enough to accom- 
modate a wheel-barrow, and after it has been balanced 
with the empty barrow on it, the record of weight of 
coal burned during the test can be easily kept. 

The same barrow should be used throughout the 
test, and to save complications in estimating the 
weight, the same number of pounds of coal should be 
filled in the barrow each load. The coal passer will 
learn in a short time to fill the barrow to within a few 
pounds of the same weight each load by counting the 
shovelsful and the difference can easily be adjusted by 
having a small box of coal near the scale from which 
to take a few lumps to balance the load, or if there is 
too much coal in the barrow some of it can be thrown 
into the box. 

At least two separate tally sheets should be provided, 
marked respectively coal and water, and the one for 
coal placed near the scale, and care should be taken 
that each load is tallied as soon as it is weighed. The 
tally sheet for water should be near the measuring 



EVAPORATION TESTS 121 

tanks and as soon as a tank is emptied it should be 
tallied. The temperature of the feed water should be 
taken at least every thirty minutes, or oftener if pos- 
sible, from a thermometer placed in the feed pipe near 
the check valve, as described in Chapter II. The 
readings should be noted and, at the expiration of the 
test, the average taken. 

If the object of the test is to ascertain the efficiency 
of the boiler and furnace it is absolutely necessary that 
the boiler and all its appurtenances be put in good 
condition, by cleaning the heating surface both inside 
the boiler and outside, scraping and blowing the soot 
out of the tubes if it be a return tubular boiler, and 
blowing the soot and ashes from between the tubes if 
it is a water tube boiler. All dust, soot and ashes 
should be removed from the outside of the shell and 
also from the combustion chamber and smoke connec- 
tions. The grate bars and sides of the furnace should 
be cleared of all clinker, and all air leaks made as 
close as possible. The boiler and all its water connec- 
tions should be free from leaks, especially the blow-off 
valve or cock. If any doubt exists as to the latter it 
should be plugged or a blind flange put on it. It is 
very essential that there should be no way for the 
water to leak out of the boiler, neither should any 
water be allowed to get into the boiler during the test 
except that which is measured by passing through the 
tanks. 

The engineer making the test should know the num- 
ber of square feet of grate surface and also the 
area of the heating surface in square feet. Rules 
for computing the latter are given in Chapter II. 
If the boiler is a water tube boiler the outside diameter 
of the tubes must be used in estimating the heating 



122 ENGINEERING 

surface. A correct knowledge of the above points is 
essential in making a test for determining any one of 
the four objects mentioned at the commencement of 
this chapter, but especially is it needed in conducting 
a test of the efficiency of the boiler and furnace. 

In making an efficiency test it is essential that the 
boiler should be run at its fullest capacity from the 
beginning to the end of the test. Therefore arrange- 
ments should be made to dispose of the steam as fast 
as it is generated. If the boiler is in a battery con- 
nected with a common header, its mates can be fired 
lighter during the test, but if there is but. the one 
boiler in use a waste steam pipe should be temporarily 
connected through which the surplus steam, if there is 
any, can be discharged into the open air through a 
valve regulated as required. Before starting the test 
the boiler should be thoroughly heated by having 
been run several hours at the ordinary rate. The fire 
should then be cleaned and put in good condition to 
receive fresh coal. 

At the time of beginning the test the water level 
should be at or near the height, ordinarily carried and 
its position marked by tying a cord around one of the 
guard rods of the gauge glass, and, to prevent all pos- 
sibility of error, the height of the water in the glass 
should be measured and a note made of it. Note also 
the time that the first lot of weighed coal is fed to 
the furnace and record it as the starting time. The 
steam pressure should be noted at the beginning of 
the test and at regular intervals during the progress of 
the test in order that the average pressure may be 
obtained. 

At the close of the test all of the above conditions 
should be as nearly as possible the same as at the 



EVAPORATION TESTS 123 

beginning; the quantity and condition of the fire 
should be the same, also the steam pressure and water 
level. This can be accomplished only by careful work 
towards the close of the test. 

During the progress of the test care should be exer- 
cised to prevent any waste of coal, especially in clean- 
ing the fire. The ash made during the test must not 
be wet down until after it is weighed, as in all calcula- 
tions for combustible and non-combustible matter in 
the coal the ash should be dry. 

The duration of the test should be at least ten hours 
if it is possible to continue it for that length of time. 
The feed pump should be kept running at such speed 
as will supply the water to the boiler as fast as it is 
evaporated, and no faster. If at the close of the test 
a portion of water is left in the last tank tallied it can 
be measured and deducted from the total. And if any 
weighed coal is left on the floor it should be weighed 
back and deducted from the total weight. If the 
boiler is fed by an injector instead of a pump during 
the test, the injector should receive steam directly 
from the boiler under test through a well protected 
pipe. Also, the temperature of the feed water should 
be taken from the measuring tanks, or at least from 
the suction side of the injector, for the reason that the 
water in passing through the injector receives a large 
quantity of heat imparted to it by live steam directly 
from the boiler. Therefore the temperature of the 
water after it leaves the injector would not be a true 
factor for figuring the evaporation. 

Determination of the Perce?itage of Moisture in the 
Steam. This is an important point in estimating the 
results of an evaporation test for the reason that each 
pound weight of moisture in the steam as it leaves the 



124 ENGINEERING 

boiler represents a pound of water that has not been 
evaporated into steam, and should therefore be 
deducted from the total weight of water fed into the 
boiler during the test. 

The steam should be tested for moisture by taking 
samples of it from the steam pipe or header as near 
the boiler as possible in order to guard against addi- 
tional moisture caused by condensation. For making 
expert boiler tests for scientific and other purposes, an 
instrument called a calorimeter is used for ascertaining 
the quantity of moisture in the steam. But most 
engineers are not so fortunate as to possess one of 
these instruments, nor even to induce their employers 
to purchase one, therefore space will not be taken up 
in describing it here. A method of testing the 
quality of the steam by noting the appearance of a 
small jet blowing into the atmosphere is mentioned 
near the close of Chapter IV, which in the absence of 
a calorimeter would answer very well for ordinary 
purposes. 

Moisture in the Coal. This can generally be obtained 
from the reports of the geologist of the state in which 
the coal is mined or from the dealer, although the 
former is the most reliable. The percentage of mois- 
ture must be deducted from the total weight of coal in 
figuring the weight of combustible. 

Measuring the Chimney Draft. A good draft is indis- 
pensable for obtaining economical results in an evap- 
oration test. The draft can be easily regulated by a 
damper to suit the conditions. Chimney draft is ordi- 
narily measured by a draft gauge connected with the 
smoke flue near the chimne}'. The usual form of draft 
gauge is a glass tube bent in the shape of the letter U. 
(See Fig. 12.) One leg is connected to the flue by 3 



EVAPORATION TESTS 



125 




small rubber hose, while the other is open to the 
atmosphere. The tube is partly filled with water, 
which will, when there is no draft, stand at the same 
height in both legs. When connected to the chimney 
or flue the suction will cause the 
water in the leg to which the 
hose is attached to rise, while 
the level of the water in the 
other leg will be equally de- 
pressed, and the extent of the 
variation in fractions of an inch 
is the measure of the draft. Thus 
the draft is referred to as being 
.5, .7 or .75 inches. The draft 
should not be less than .5 inches 
in any case to insure good results. 

Having thus successfully con- 
ducted the test to its close, and 
being armed with all the data 
heretofore noted, the engineer 
is now ready to compute the 
results. 

If the test is made for the pur- 
pose of determining the effi- 
ciency of the boiler and setting 
as a whole, including grate, 
chimne}^ draft, etc., then the 
result must be based upon the 
number of pounds of water evap- 
orated per pound of coal. This latter phrase includes 
not only the purely combustible matter in the coal, 
but the non-combustible also, as ash, moisture, etc. 
Some varieties of western coal contain as high as 12 to 
14 per cent, of moisture, and the ability of the furnace 




FIGURE 12. 



126 ENGINEERING 

to extract heat from the mass is to be tested, as well 
as the ability of the boiler to absorb and transmit that 
heat to the water. Therefore the efficiency of the 
boiler and furnace = 

Heat absorbed per pound of coal. 
Heating value of one pound of coal. 

If the test is to determine the efficiency of the boiler 
itself as an absorber of heat, then the combustible 
alone must be considered in working out the final 
result. Thus, 

Efficiency of boiler = 

Heat absorbed per pound of combustible. 
Heating value of one pound of combustible. 

When making a series of tests for the purpose of 
comparing the economical value of different varieties 
of coal the conditions should be as nearl}^ uniform as 
possible; that is, let the tests be made under ordinary 
working conditions and with the same boiler or boil- 
ers, and if possible with the same fireman. 

The following is a record of one of many evapora- 
tion tests made by the author, and is introduced here 
for the purpose of illustrating methods of computing 
the results to be obtained from the various data. The 
rather large quantity of coal burned per square foot of 
grate surface per hour (25 lbs.) is owing to the fact 
that the boiler was run to its full capacity, the coal 
burning clean and forming no clinker. The chimney 
draft also was exceptionally good, giving a large unit 
of evaporation per square foot of heating surface per 
hour. The low temperature of the escaping gases is 
due to the fact that they were returned over the top of 
the boiler before passing to the chimney. 



EVAPORATION TESTS 127 

Date of test 

Duration of test, 12 hours. 
Boiler, return tubular, 72 in. diameter, 18 ft. long, 62-41^ in. tubes. 
Kind of coal, Pocahontas; average steam pressure.. 85 lbs. 

Weight of coal consumed 11 , 100 

Weight of water apparently evaporated 107,187 

Weight of dry ash returned 8.1 per cent.= goo 

Moisture in the coal 2.0 " = 222 

Moisture in the steam 1.0 " = 1,071 

Dry coal corrected for moisture . . 10,878 

Weight of combustible 9,978 

Water corrected for moisture in the steam 106,116 

Water evaporated into dry steam, from and at 212 . . 117,788 
Water evaporated per lb. of coal, actual conditions. . 9.65 

Water evaporated per lb. of coal, from and at 212 . . 10.61 

Water evaporated per lb. of combustible, from and 

at 212 11. 81 

Water evaporated per lb. of dry coal, from and at 212° 10.82 

Water evaporated per hr. per sq. ft. of heating surface 6. 22 

Coal burned per sq. ft. of grate surface per hour .... 25 

Horse power developed by boiler during test 284.5 

Temperature of feed water, average 141 ° 

Temperature of chimney gases, average 400 

Square feet of grate surface 36 

Square feet of heating surface 1576 

Ratio of grate surface to heating surface 43.7 

The results obtained will be taken up in their regu- 
lar order beginning with, first, water evaporated into 
dry steam from and at 212 . As it may be of benefit 
to some, a short definition of the meaning of the above 
expression is here given. 

The term "equivalent evaporation," or the evapora- 
tion from and at 212 , assumes that the feed water 
enters the boiler at a temperature of 212 and is evap- 
orated into steam at 212 temperature and at atmos- 
pheric pressure. As for instance, if the top man hole 
plate were left out or some other large opening in the 
steam space allowed the steam to escape into the 
atmosphere as fast as it was generated. Owing to 
the variation in the temperatures of the feed water 
used in different tests, and also the variation in the 
steam pressure, it is absolutely necessary that the 



128 ENGINEERING 

results of all tests be brought by computation to 
the common basis of 212 in order to obtain a just 
comparison. 

The process by which this is done is as follows: 
Referring to the record of th£ test it is seen that the 
steam pressure average was 85 lbs. gauge pressure, or 
100 lbs. absolute, and that the temperature of the feed 
water was 141 °. Referring again to Table No. 5, phys- 
ical properties of steam, it will be seen that in a pound 
of steam at 100 lbs. absolute pressure there are 1,181.8 
heat units, and in a pound of water at 141 ° temperature 
there are 109.9 heat units. It therefore tooku8i.8- 
109.9 = I07I-9 heat units to convert one pound of feed 
water at 141 ° into steam at 85 lbs. pressure. To con- 
vert a pound of water at 212 into steam at 
atmospheric pressure, and 212 temperature requires 
965.7 heat units, and the 1,071.9 heat units w T ould evap- 
orate 1,071.9 + 965.7 = 1. 11 lbs. water from and at 212 . 
The 1. 1 1 is the factor of evaporation for 85 lbs. gauge 
pressure and 141 ° temperature of feed water, and by 
multiplying "water corrected for moisture in the 
steam" (see record of test), 106,116 lbs., by 1.11, the 
weight of water which could have been evaporated into 
steam from and at 212 , is obtained, which is 117,788 
lbs. The factor of evaporation is based upon the 
steam pressure and the temperature of the feed water 
in any test and the formula for ascertaining it is as 

follows: Factor = —? , in which H = total heat in 

965.7 

the steam, and h = total heat in the feed water. It 
is used in shortening the process of finding the evap- 
oration from and at 212 , and Table No. 6 gives the 
factor of evaporation for various pressures and tem- 
peratures. 



EVAPORATION TESTS 



129 



Table 6 
Factors of Evaporation 



u V 


X 


X 


X! 


X 


i 


X 


X 


XI 


X 


►? rt 


3 iri 


%S 


S R 




| a 


bt>~° 


bo's 


So 8 


80 S- 






^ r/i 






as tfl 


03 . 






rt . 


1 B 


^ g 


<S 8 


^ £ 


^ s 


g 


O g 


O gj 


£ 


O % 






















fen 


D-, 


Ph 


P4 


Ph 


£ 


£ 


£ 


£ 


£ 


212° 


I.027 


1.030 


1.032 


I-035 


1.037 


I.O39 


1. 041 


1.043 


1.047 


200° 


I.O39 


1.042 


I.045 


I.O47 


1.050 


I.052 


1.054 


1.056 


1.059 


I 9 I° 


I.O49 


1.052 


I.054 


I.057 


1.059 


I. 06l 


1.063 


1.065 


1.069 


182° 


I.O58 


1. 061 


I.O64 


I.066 


1.069 


I. 07I 


r.073 


1.075 


1.078 


173° 


I.067 


1.070 


1.073 


I.O76 


1.078 


I.OSO 


1.082 


1.0S4 


1.087 


164 


I.077 


1.080 


I.O83 


1.085 


1.087 


I.O9O 


1. 091 


1.093 


1.097 


152 


I.089 


1.092 


1-095 


I.09S 


1. 100 


1,102 


1. 104 


1. 106 


1. 109 


H3° 


I.O99 


1. 102 


1. 105 


I. I07 


1. 109 


I. Ill 


1. 113 


1.115 


1. ng 


134° 


I. IO8 


1. in 


1. 114 


I. Il6 


1. 119 


1. 121 


1. 123 


1. 125 


1. 128 


125° 


I.II8 


1. 121 


1. 123 


I. 126 


I. 128 


1. 130 


1. 132 


1134 


1. 137 


113° 


I. I30 


i.133 


1. 136 


I. I38 


1. 140 


I- 143 


1. 145 


1. 146 


1. 150 


104° 


1. 138 


1. 142 


1. 145 


I. I48 


1. 150 


1. 152 


1154 


1. 156 


1. 159 


95° 


1. 149 


1. 152 


i- 154 


T.I57 


I- 159 


I.l6l 


1. 163 


1. 165 


1. 169 


86° 


I.I58 


1. 161 


1. 164 


I. 166 


1. 169 


I.I7I 


1. 173 


1. 174 


1. 178 


77° 


1. 167 


1. 170 


I.I73 


1.176 


1. 178 


I. ISO 


1. 182 


1. 1 84 


1. 187 


65° 


1. 180 


1. 183 


1. 186 


I. 188 


I. T90 


I. I92 


1. 194 


1. 196 


1.200 


56° 


1. 189 


1. 192 


1. 195 


I. 197 


1.200 


I.202 


1.204 


1.206 


1.209 


47° 


1. 199 


1. 201 


1.204 


I.207 


1.209 


I. 211 


1. 213 


1. 215 


.1.218 


38° 


1.208 


1. 211 


1. 214 


I. 2l6 


1. 218 


I.220 


1.222 


1.224 


1.228 



Second, water evaporated per pound of coal actual 
conditions = water apparently evaporated divided by 
coal consumed = 9.65 lbs. No accurate estimate 
regarding the quality of the coal or the efficiency of 
the boiler can be made from this figure (9.65 lbs.). It 
can be used, however, in estimating the cost of fuel for 
generating the steam; as, for instance, if the boiler is 
supplying steam to an engine that uses 30 lbs. of steam 
per horse power per hour, it will require 30 -s- 9.65 = 3.1 
lbs. of coal per horse power per hour; the "actual 
conditions" under which the boiler is being operated 
being the pressure of steam required by the engine 
and the temperature of the feed water. 



1 30 ENGINEERING 

Third, water evaporated per pound of coal from and 
at 212° = water evaporated into dry steam from and at 
212° divided by coal consumed = 10.61 lbs. This fig- 
ure is the proper one to use in comparing the relative 
economic values of different varieties of coal tested 
with the same boiler or boilers. 

Fourth, water evaporated per pound of combustible 
from and at . 212 = water evaporated into dry steam 
from and at 212 divided by weight of combustible 
= 1 1. 81 lbs. This result is the one to be used for 
ascertaining the efficiency of the boiler, and the per- 
centage of efficiency is found by. dividing the heat 
absorbed by the boiler per pound of combustible by 
the heat value of one pound of combustible. The 
average heat value of bituminous and semi-bituminous 
coals is not far from 15,000 heat units per pound of 
combustible. In the evaporation of 11. 81 pounds of 
water from and at 212° the heat absorbed was 11. 81 x 
965.7= 11,404.9 heat units. The efficiency of the boiler 

,, r 11,404.9X100 „*■ . 

therefore was 1500J — = 76 per cent. 

In like manner to ascertain the efficiency of the 
boiler and furnace as a whole, the water evaporated 
from and at 212 per pound of coal is taken. Thus, 
10.61 x 965.7 = 10,246 heat units absorbed from each 
pound of coal. Now assuming that there were 13,500 
heat units in each pound of the coal used in the test, 
the per cent of efficiency of boiler and furnace was 

10,246X100 

13,500 ~ 75- 9- 

Fifth, water evaporated per pound of dry coal from 
and at 212 = water evaporated into dry steam from 
and at 212 divided by coal corrected for moisture. 

Thus, 117,788 -5- 10,878 = 10.82 lbs. This result is useful 
for calculating the results of tests of the same grade 



EVAPORATION TESTS 131 

of coal, but differing in the degree of moisture in 
each. 

Sixth. Boiler horse power. The latest decision of 
the American Society of Mechanical Engineers (than 
whom there is no better authority) regarding the horse 
power of a boiler is as follows: "The unit of commer- 
cial horse power developed by a boiler shall be taken 
as 34^ units of evaporation per hour. That is, 34^ 
lbs. of water evaporated per hour from a feed temper- 
ature of 212 into steam of the same temperature. 
This standard is equivalent to 33,317 B. T. U. per hour. 
It is also practically equivalent to an evaporation of 
30 lbs. of water from a feed water temperature of ioo° 
F. into steam of 70 lbs. gauge pressure." 

According to this rule the horse power developed 
by the boiler during the test under consideration = water 
evaporated into dry steam from and at 212 , 117,788 
lbs ■*■ 12 hrs. •*■ 34. 5 = 284.5 horse power. 

Questions 

1. What is the primary object of an evaporation 
test? 

2. Name four other important points which can be 
determined by evaporation tests. 

3. In making a test of the efficiency of the boiler 
and furnace, what precautions should be observed? 

4. How is the heating surface of water tube boilers 
estimated? 

5. What length of time should a test be conducted? 

6. In case the boiler is fed by an injector, what pre- 
cautions are necessary? 

7. If the steam contains any moisture, what should 
be done? 

8. How is the weight of combustible determined? 



132 ENGINEERING 

g. What is a calorimeter, and for what purpose is it 
used? 

io. By what other method may the moisture in the 
steam be estimated approximately? 

11. What should be done with the percentage of 
moisture in the coal? 

12. How is the chimney draft measured? 

13. Describe a draft gauge. 

14. Give the formula for ascertaining the efficiency 
of the boiler and setting. 

15. If the test is to determine the efficiency of the 
ooiler alone, what factors are used? 

16. If a series of tests is made for comparing differ- 
ent varieties of coal, what should be done? 

17. What is meant by equivalent evaporation? 

18. Why should the results of all tests be computed 
from and at 212 ? 

ig. What is a factor of evaporation? 

20. How is it determined? 

21. What is a boiler horse power? 

22. How many heat units per hour is this equiv- 
alent to? 



CHAPTER VI 

VALVES AND VALVE SETTING 

Valves and valve setting — Importance of correct adjustment — The 
D slide valve — Single valve engines— Four valve engines — 
Various positions of the slide valve during one revolution — 
Relative positions of the crank pin and eccentric during the 
stroke — Valve diagrams — Placing the engine on the center — 
Adjusting the length of eccentric rod — Measuring the inside 
and outside lap — Setting the valve — Fixed cut off engines — 
Variable automatic cut off —Factors affecting the distribution 
of the steam — Why the four valve engine is the most eco- 
nomical — Description of corliss valves and valve gear and 
directions for adjusting the same. 

Valves and Valve Setting. It goes without saying that 
every man who aspires to be an engineer should en- 
deavor to thoroughly acquaint himself with the princi- 
ples governing the action of valves as well as the details 
of valve setting. But it must be remembered that this 
knowledge can not be acquired in a day or a week, or 
even months. True, a man maybe able to learn some 
of the alphabet of valve lore in a comparatively short 
time, but the more practical experience he has in the 
work the more will he realize the supreme need of 
mastering all the details of the process. 

The common D slide valve, simple as it appears, is 
capable of furnishing problems over which savants 
have puzzled themselves. 

The development of the full amount of power of 
which the engine is capable, its efficiency and eco- 
nomical use of steam, and its regular and quiet action 
are, in the largest degree, dependent upon the correct 
adjustment of its valve or valves. 
133 



134 ENGINEERING 

There are many different types of valves for control- 
ling the admission and release of steam to and from the 
cylinders of engines, but the basic principles govern- 
ing the adjustment of all, whether slide, poppet, rota- 
tive, piston, etc., are exemplified in the action of the 
common D slide valve, viz., the admission of the 
steam to the cylinder, its cut off and release, and 
the closure of the exhaust, each and all of which 
events are to take place at the proper moment during 
one stroke of the piston. 

In order to properly perform these important func- 
tions the valve must have lead and lap. The various 
terms relating to valve action are plainly defined 
in Chapter VIII on "Definitions," and it is unnec- 
essary to repeat them here. If the outside lap is 
increased admission will be later and cut off earlier, 
and if it be desired to keep the lead the same it will be 
necessary to move the eccentric forward, which will 
make the other events, cut off, release, and compres- 
sion, earlier also. If the inside lap is increased the 
result will be an earlier closing of the exhaust and 
increased compression. 

These propositions refer mainly to engines of the 
single valve variety in which one valve controls the 
admission and distribution of the steam for both ends 
of the cylinder. In engines of the four valve type, 
having a separate steam and exhaust valve for each 
end of the cylinder, each individual valve may be 
adjusted independently of the others, as will be 
explained later on, and in the case of engines having 
separate eccentrics, one for the steam and one for the 
exhaust valves, the adjustment becomes still more 
perfect. 

We will first study the action of the D slide valve by 



VALVES AND VALVE SETTING 



135 



referring to Fig. 13, which is a sectional view of a 
valve, valve seat and ports. The valve is represented 
at mid travel or in its central position. S P, S P are 
the steam ports, and E P is the exhaust port. The 
projections marked X at each foot of the arch inside 



L 

1 1 

1 1 


s*^ 


L 

1 | 
l | 
1 


' ' k 


^^^^ 


\ l 


' ' ^S 


*L* *A 




JP^i 


FIGURE 13. 


W p y@ 



the valve, represent inside lap and may be added to or 
taken from the inside edges of the valve, according as 
more or less compression is desired. The dotted lines, 
L, L represent outside lap. 

Motion is imparted to the valve through the medium 



leaoT 




FIGURE 14. 



of the eccentric. If the valve had neither lap nor lead 
the position of the eccentric on the crank shaft would 
be just 90 or one-quarter of a circle ahead of the 
crank, but as more or less lap as well as lead is 
required, it becomes necessary to move the eccentric 



136 ENGINEERING 

still farther ahead of the crank, and this farther 
advance is termed angular advance, lap angle for lap 
and lead angle for lead. 

Assuming the piston to be at the end of the stroke 
towards the crank, in other words, the engine to be 




on the dead center, the first function of the valve is 
lead or admission, illustrated by Fig. 14. Owing to 
the valve having both lap and lead, the position of the 
highest point of the eccentric will be assumed in this 
case to be 120 ahead of the crank, the position of the 
latter being at o°. 

Exhaust opening has also occurred at the opposite 




FIGURE 16. 

end of the cylinder. The second function is full port 
opening, Fig. 15, the crank having moved through 60 ° 
and the eccentric is now at 180 , the farthest point of 
its throw in that direction, the valve being at the end 
of its travel. At this point it might be well to note a 



VALVES AND VALVE SETTING 



137 



matter about which some persons are liable to become 
confused, simple as it is, viz., that the travel of a slide 
valve equals twice the port opening plus twice the out- 
side lap. For instance, suppose the width of each 
steam port to be \% in. and the outside lap to be I in. 
In Fig, 15 the valve is at the extreme end of its travel 




FIGURE 17. 

towards the right and is about to return. It first 
covers port number one = \% in. Next it moves to 
mid travel lap number one = 2% in. Its next move is 
lap number two = 3^ in., and lastly it uncovers port 
number two = 4^ in., which is its travel. 
To return to the third function of the valve or cut 




FIGURE 18. 

off, Fig. 16. The crank has now traversed 120 and 
the highest point of the eccentric is at 60 ° on the 
return circle, a point equivalent to 240 ° of the circle 
described by the crank. 

The fourth function is when compression begins at 
the head end of the cylinder, Fig. 17. The crank is 



138 



ENGINEERING 



now at 150 , the piston being near the end of the stroke 
and the eccentric has reached 90 of the return circle 
or three-quarters of the crank circle, while the crank 
has still to travel 30 in order to complete the first one- 
half of its circle. At this point we can study the effect 
of inside lap, because if the valve has no inside lap, 
release on the crank end will begin almost at the same 
moment that compression takes place at the head end, 




/to' 



90* 

FIGURE 19. 



but by adding inside lap, compression can be caused 
to take place earlier and release later. 

The next event is admission at the head end of the 
cylinder, Fig. 18. The crank has now arrived at 180 , 
having completed one-half of a revolution; the piston 
is at the end of the stroke, and the eccentric is at 
120 on the return path. Fig. 19 serves to better illus- 
trate the relative positions of the crank pin and 



VALVES AND VALVE SETTING 189 

eccentric during the stroke. The inner circle repre- 
sents the path described by the high point of the 
eccentric, and the large circle that of the crank pin. 
The radius C 2 of the small circle represents the throw 
of the eccentric, and the distance C L is the lap of the 
valve plus the lead. The point of intersection of the 
vertical line, L 1, with the eccentric circle locates the 
position of the highest point of the eccentric, and 
the line C B, drawn from the center of the crank shaft 
through this point, indicates the angular advance, 
which in this case is 30 represented by the angle 
ABC. The figures 1, 2, 3, 4, 5 indicate the position 
of the high point of the eccentric at the moment of 
each function of the valve. The action of the valve 
can be moregraphically illustrated by means of valve 
diagrams, of which there are several different kinds, 
notably the Bilgram and Zeuner. The Zeuner dia- 
gram will be made use of in this instance. 

Fig. 20 shows the total movement of the valve, 
regardless of lap and lead. First draw line C 1 to 
represent the center line of the engine. Next draw 
line C 4 perpendicular to the line of centers, with C as 
the center of the crank shaft. The radius of the semi- 
circle D, 1, 2, 3, 4,^5, 6 equals the radius of eccentri- 
city. Line C D represents the position of the crank 
when the valve is at mid travel or in its central posi- 
tion, D being the location of the crank pin. Referring 
back to Fig. 13 the valve is there shown in its central 
position and supposed to be moving in the direction of 
the arrow in order to admit steam to the crank end ot 
the cylinder. Again referring to Fig. 20, draw line 
C A in such a position that the angle ABC will 
equal the angular advance of the eccentric, which we 
will assume in this case to be 30 . . This will bring the 



140 



ENGINEERING 



high point of the eccentric at B while the crank, as 
before stated, is at D. Next using line C A as the 
diameter draw a circle about it called the valve circle. 



A, 



[Tfi- 



C\ 






\ 



**■" 



Va}vs Ttavet = ?%* 

FIGURE 20. 



Now suppose the crank to be turning in the direction 
of the arrows. At position D the crank line is just 
about to cut into the valve circle, the valve being 
central. When the crank gets to position I the valve 



VALVES AND VALVE SETTING 141 

has moved the distance C E. When the crank is at 2 
the valve has moved the distance C M, and when the 
crank arrives at 3 the valve has moved to the limit of 
its travel from its central position and it now begins 
the return movement. The motion of the valve is 
comparatively slow at this point for the reason that the 
high point of the eccentric is now passing the center 
at 7. The distance the valve has moved backward 
while the crank has moved from 3 to 4 is the distance 
B F, while F C represents its distance from the central 
position, and G C the same when the crank is at 5. 
When the crank arrives at 6 and its line has left the 
valve circle, the valve is again central. Fig. 20 merely 
shows the movement of the valve through one-half of 
its travel without giving any details regarding port 
openings, cut off, etc. 

In Fig. 21 the influence of outside lap is delineated. 
According to the dimensions of the valve under con- 
sideration the outside lap is one inch. The diagram is 
drawn precisely as in Fig. 20, and in addition strike an 
arc representing the outside lap, using C as the center 
with a radius equal to the outside lap. As before, the 
crank is at D and the valve central. When the. crank 
has moved to E and its line cuts the intersection of 
the outside lap and valve circles, the valve has moved 
the distance C H, just equal to the outside lap, and 
the port begins to uncover at this point. Then by the 
time the crank gets to the center, 1, the port is open' 
the distance L O, which is the lead, in this case yi in. 
This position of the valve is shown in Fig. 14. 

The position of the crank when cut-off takes place is 
ascertained by drawing a line, C G 5, through the inter- 
section of the outside lap and valve circles, where the 
valve is on its return movement (see Fig. 16). Thus 



Wl 



ENGINEERING 



far no account has been taken of release and compres- 
sion, and in order to determine the position of the 
crank when these events occur it will be necessary to 







=* Z?*'* 



/ — 

FIGURE 2L 

draw the valve circle for the opposite movement of the 
valve, for be it remembered that the movement of the 
valve so far considered has been only one-half of its 



VALVES AND VALVE SETTING 



143 









1 






\><> 


i / I \ 




/ \\T\ 


Je )%T \ 




/l/ji^' 


7 




Xm/. ^\ 




S 






\<2 x J 7->L 






1 ^^y^t 


X/q '\ 






\^^"""~^ s^/l f J %s 


7&y \ 


1 


e 










\ 

10 


A-? \ 
ft \ 


















Vedve 7kaveC 


= «t'~ \ 








latrurof ?ecenit< ct 


^ = *v V 








Out-r/tte £oa 








bir</>e La/> 


= A- ^ 


\ 




f'/ect/rt L eac/ 


- \~ 





FIGURE 22. 



travel; that is, it has moved from its central position 
towards the head end of the cylinder and back again. 
We have seen how it has thus performed the functions 



] 44 ENGINEERING , 

of admission, full port opening and cut off for the 
crank end of the cylinder, and now by referring to 
Fig. 22 it will be seen at what point of the stroke tJru 
remaining events, viz., release and compression, 
occur. 

Draw a second valve circle, Fig. 22, diametrically 
opposite the first. Also draw an arc with a radius 
equal to the inside lap, which in this case is assumed 
to be one-half inch. When the crank gets to the 
position 7 its center line cuts the intersection of the 
inside lap and valve circles and release begins. When 
the crank arrives on the center 8, the valve has moved 
the distance C T from central position; but C X of this 
distance has been occupied by the inside lap, therefore 
the lead on the exhaust is represented by the distance 
X T. When the crank on its return stroke arrives at 
the position marked 10, its line again cuts the inter- 
section of the inside lap and valve circles and com- 
pression takes place, as in Fig. 17. By dropping 
perpendiculars from the positions of the crank at 1, 5, 
7 and 10 an indicator diagram may be drawn showing 
the performance of an engine with this style of valve. 

Fig. 23 shows the effect of decreasing the angular 
advance, that is, setting the eccentric back towards the 
crank. In this instance the eccentric is set back io°, 
thus making the angle of advance 20 instead of 30 as 
before. The full lines represent the new angle, while 
the dotted circles and lines indicate the valve and its 
movements as drawn at first. A shows the original 
point of admission and A' the position of the crank 
when admission takes place with the lesser angle of 
advance. Similarly R and R' show the old and new 
points of release, and C and C the compression The 
two different points of cut off are also indicated. It 



VALVES AND VALVE SETTING 



145 



will be observed that all of these events occur later 
and the lead also is diminished. 

In locomotives, and also in some types of adjustable 
cut off engines, the travel of the valve may be varied 
at will, and the effect of decreasing the valve's travel 






TO 



/^^ 



FIGURE 23. 



is illustrated by Fig. 24, the full lines showing the 
decreased travel and its influence, and the dotted lines 
showing the original. Admission and release occur 
later, while cut off and compression take place earlier, 
and the lead is less. The travel of the valve as indicated 



146 



ENGINEERING 



in Fig. 24 has been decreased one inch, making it 3^ 
in. in place of 4^ in. as before. 

Fig. 25 shows the result of increasing the outside 
lap. The lap has been increased in this case from 1 
in., as originally drawn, to 1% in. as indicated by the 



C ' 



W 



'17 



FIGURE 24 

full lines, while the dotted lines show the lap as it was 
before being changed. The effect of this change is to 
cause less lead, a later admission and an earlier cut 
off, but compression and release are not affected for 
the reason that these latter events are controlled by 
the inside lap, which has not been changed, 



VALVES AND VALVE SETTING 



147 



In Fig. 22 the valve is shown as cutting off the steam 
when the crank has completed 120 or two-thirds of 
the half revolution, but the point of cut off on the indi- 
cator diagram shows that the piston has traveled I of 
the stroke. This discrepancy is due to the obliquity 



/€*■ 



&& 



.*y 



FIGURE 25. 



of the connecting rod, as it will be seen by looking at 
the valve diagram, Fig. 22, that the crank must travel 
farther to complete the stroke from this point than the 
piston does. In order to cause the valve to cut off 
earlier, say at one-half stroke, it will be necessary to 
do one of two things, either to increase the outside 



148 



ENGINEERING 




FIGURE 26. 



lap, which would have a tendency to cause admission 
to occur too late, or the angle of advance may be 



VA1/VES AND VALVE SETTING 149 

increased sufficient to cause cut off to take place at 
half stroke, but to do this alone would cause admission 
to occur too early. Therefore the proper thing to do 
is to increase both the angle of advance and the out- 
side lap. Fig. 26 shows how this can be done without 
decreasing the travel of the valve. The angle of 
advance, A B C, is now 50 , where before it was 30 , 
as in Fig. 22. 

The valve is central when the crank is at position 1; 
the high point of the eccentric being at point 4. The 
outside lap which before was 1 in. has had ^\ in. added 
to it, making it i T 7 g- in. When the crank gets to D the 
port is just commencing to open, and with the crank 
on the center at 2, the lead is }( in. 

It will readily be seen at this point that by increasing 
the outside lap still more the lead can be diminished, 
and the point of cut off made still earlier, but this 
would result in a still further reduction of the power of 
the engine, which has already been considerably 
reduced, as shown by the diminished area of the indi- 
cator diagram as compared with the one in Fig. 22. 
When the crank gets to position 3 the valve has 
reached the limit of its travel, and the port is open the 
distance A a, which is as far as the outside lap will 
permit. With the crank at point 4 cut off occurs. But 
with the increased angular advance and the inside 
lap remaining as it was before, viz., j4 in., release 
would occur too early. Therefore it will be nec- 
essary to increase the inside lap sufficient to cause 
release and compression to take place at as near 
the proper points as possible. In this instance 3/s 
in. has been added, making the inside lap 7^ in., 
and release takes place with the crank at position 5, 
while compression begins at 6. These points may 



150 



ENGINEERING 



also be changed by simply adding to or decreasing 
the inside lap. 

It should be noted that in the foregoing discussion 
of valve gear it is understood that the valve stem 
moves in the same direction as the eccentric rod, that 
is, the direction of motion is not reversed by a rocker 
arm interposed between the eccentric and the valve. 



r 




FIGURE 27. 

In case there should be a rocker arm connected so as 
to reverse the motion and thereby cause the valve to 
move opposite to the eccentric rod, it will be neces- 
sary to set the eccentric behind the crank, as in Fig. 27. 
Most engines are fitted with a rocker arm for trans- 
mitting the motion of the eccentric to the valve stem, 



r 




FIGURE 28. 



but the usual practice is to attach them so that the 
direction of motion is not reversed, as in Fig. 28 

The first step in the operation of valve setting is to 
place the engine on the dead center, which means that 



VALVES AND VALVE SETTING 15 1 

the piston is at the end of the stroke, and the centers 
of the main shaft, crank pin and crosshead pin, or 
wrist pin as it is sometimes called, are in line (see Fig. 
31). When moving the engine to place it on the cen- 
ter it should always be turned in the direction in which 
it is to run. This is to guard against any errors which 
might result from lost motion or looseness in the 
reciprocating parts. Turn the fly wheel around until 
the crosshead is almost to the end of the stroke, say 
within a half inch of it, as at A, Fig. 29. Then with a 




figure 29. 

steel scriber or penknife mark the location of the 
crosshead on the guides A, also provide a secure rest- 
ing place upon the floor of the engine-room for a 
markef to be placed against the rim of the wheel. 
This rest should be firmly fastened to the floor in order 
that its position may not be changed during the opera- 
lion of valve setting. Place the marker against the 
wheel as at B and mark the point with a center punch 
or cold chisel. Next turn the engine carefully until 
the crosshead completes the stroke and moves back on 
the return stroke until the mark A is in line again. 
Make another mark on the rim of the wheel opposite 
the marker at C. This position of the engine is 
shown in Fig. 30, and it will be seen that the crank is 
now as much above the center as it was below in Fig. 



152 



ENGINEERING 



29. Now with a pair of large dividers ascertain the 
middle or half distance between marks B and C and 
put another mark, D, at this point. Then turn the 




FIGURE 30. 

engine a complete revolution until mark D comes 
opposite the pointer, Fig. 31, and the engine will be 
on the true center. 

At this point the question may arise, why not simply 
reverse the motion and back the wheel up until the 
mark D is in line with the marker? The answer is, 




figure 31. 



that while this would undoubtedly save considerable 
labor, yet it would almost certainly result in an error, 
on account of the lost motion of the moving parts 
which would permit of considerable movement of the 
wheel before any movement of the crosshead would 
take place if the wheel was turned back. The result 
would be that when mark D came to be opposite to the 



VALVES AND VALVE SETTING 



1.53 



pointer, the crank would not be on the true center. 
The next move is to see that the eccentric rod is 
adjusted to the proper length. If there is a rocker 
arm, connect the eccentric rod in its proper place, 
leaving the valve rod disconnected for the time being. 






^ 



£eceni/i/c &><* 



t 






K.y 



\ 



FIGURE 32. 



Then adjust the length of the rod so that when the 
eccentric is turned around on the shaft the rocker arm 
will vibrate equal distances on each side of a plummet 
line suspended through the center of the pin upon 
which the arm turns, as in Fig, 32. Before connecting 



154 



ENGINEERING 



the valve rod the valve should be put in its central 
position and marked. To do this it will be necessary 
to first ascertain the outside lap. 

The most accurate method of doing this is to take the 
valve out and measure the distances between the out- 
side edges of the steam ports as at B, Fig. 33. Then 
measure the width of the valve from edge to edge as 
at A. Then A - B + 2 = the outside lap. For instance, 
A = 8.5 in., B-6.5 in. Then 8.5-6.5-2, and 2 




FIGURE 33. 



divided by 2 = 1 in., which is the lap. The inside lap. 
should also be measured at this point for convenience, 
and the measurements preserved for future reference. 
The inside lap is ascertained by measuring the distance 
between the inside edges of the ports and the distance 
across the arch of the valve from one inside edge to 
the other (see Fig. 33) and dividing the difference 
by 2. For instance, the distance F is 4 in., and E is 
3 in. ; then A ^ = .5 in., making the inside lap }4 in. 
To place the valve central, measure the width of the 



VALVES AND VALVE SETTING 155 

outside lap each way from the outside edges of the 
steam ports and mark the points on the valve seat with 
a sharp lead pencil. Then place the valve with edges 
on the marks and it will be central. To insure accu- 
racy measurements should also be taken from the out- 
side edges of the steam ports to the ends of the seats. 
Having fixed the valve in its central position, replace 
the stem and if it is secured in the valve by nuts, as in 
Fig. 33, care should be taken to leave a little play for 
the valve between the nuts, otherwise it is liable to 
become stuck and held off the seat when it gets hot 
and expands. Make a, center punch mark C, on the 
edge of the valve chest directly over the valve stem, 
and placing one leg of a tram or pair of dividers in the 
mark, with the other leg describe a mark on the top of 
the Valve as at D, thus marking the valve in its central 
position. 

Now with the rocker arm perpendicular, the eccen- 
tric rod having been previously adjusted, connect the 
valve rod to the rocker, and turn the eccentric to the 
limit of its throw in one direction, and measure 
the distance the valve has traveled from its central 
position. Then turn the eccentric around to its 
extreme throw in the other direction, and if the valve 
travels the same distance from its central position in 
the opposite direction the lengths of the rods are cor- 
rect, but if not correct the necessary change can 
usually be made by shifting the nuts on the valve stem, 
or if the valve is secured to the stem by a yoke the 
change can be made in the rod. 

Having succeeded in getting the correct travel for 
thejvalve, the next step is to set the eccentric. With 
the engine -on the dead center, turn the eccentric 
around on the shaft in the direction in which the 



156 ENGINEERING 

engine is to run, so as to take up all the play in the 
valve stem and other moving parts, and with the tram 
or dividers watch the valve until it has moved away 
from its central position by the amount of its outside 
lap, plus the lead it is desired to give the valve. For 
instance, if the valve has one inch outside lap and the 
lead is to be }i in., the valve should be moved away 
from its central position 1^5 in., and also away from 
the end of the cylinder at which the piston is. The 
steam port for that end should now be open }i in., and 
the eccentric should be ahead of the crank one-quarter 
turn plus the angular advance required for the outside 
lap and lead, or if as previously explained, the motion 
of the eccentric is reversed by a rocker arm the eccen- 
tric should be behind the crank by the same amount. 
Tighten the set screws holding the eccentric on to the 
shaft and turn the engine around until it is on the 
opposite center. Then if the lead is the same on each 
center the valve is set correctly. If the lead is not the 
same, move the valve on the stem toward the end 
having the most lead, a distance equal to one-half the 
difference between the two leads. If the lead as 
equalized is more than is desired, move the eccentric 
back on the shaft until the correct lead opening is 
secured, then tighten the set screws permanently, and 
with a sharp cold chisel make a plain mark on the 
shaft and opposite to this another mark on the 
eccentric. This will save considerable trouble in case 
the eccentric should slip or be accidentally moved 
from its true position at any time. 

Although the common D slide valve as applied to 
stationary engines usually has its point of cut off 
fixed, yet there are many types of variable automatic 
cut off engines with single slide valves of various pat- 



VALVES AND VALVE SETTING 157 

terns, such as box valves in which the steam passes 
through the valve, piston valves in which the steam 
either passes through or around the ends of the valve, 
so-called gridiron valves and various other types. 
Such valves are generally applied to high speed 
engines and are actuated by eccentrics which are 
under the control of shaft governors which vary the 
position of the eccentric with relation to the crank 
according to the load that is on the engine, thus regu- 
lating the point of cut off so as to maintain a constant 
speed, while the throttle is kept wide open. While 
the details of setting all the various styles of valves, 
including the corliss or four valve type, differ consider- 
ably from those required in setting the D valve, yet 
the same principles govern the operation, no matter 
what kind of a valve is to be adjusted 

In all types of reciprocating engines the same fac- 
tors affecting the distribution of the steam are present, 
viz., the outside or steam lap affecting admission and 
cut off, and the inside or exhaust lap affecting release 
and compression. While the D valve (and other 
types of single valves) combines these four principal 
factors within itself (that is, two steam laps and two 
exhaust laps), it should be noted that in the four valve 
type of engine the same factors are distributed among 
four valves, each valve performing its own particular 
function in controlling the distribution of the steam 
for the end of the cylinder to which it is attached. 
Also each valve may be adjusted to a certain degree 
independently of the others, and this fact goes far 
towards explaining why engines of this type, with the 
disengaging valve gear, are so much more economical 
in the use of steam than are those with the ordinary 
fixed cut off. Thus, for instance, the steam valves of 



158 



ENGINEERING 



a corliss engine may be adjusted to cut off the steam 
at any point, from the very beginning up to one-half 
of the stroke, without in the least affecting the release 
or compression because these events are controlled by 
the exhaust valves. 

As the corliss engine is a prominent and familiar 
type of the four valve detaching cut off engine, and 
embodies the main features of nearly all engines 
belonging to that class, it will be used to illustrate the 
method of setting the valves on a four valve engine. 




figure 34. 



Fig. 34 is a sectional view of the cylinder, steam and 
exhaust chests, and the valve chambers of a corliss 
engine. I and 2 are the steam valves and 3 and 4 the 
exhaust valves. The valves work in cylindrical cham- 
bers accurately bored out, the face of the valve being 
turned off to fit steam iight. They are what is termed 
rotative valves, that is, they receive a semi-rotary 
motion from the wrist plate, which in turn is actuated 
by the eccentric. 

In some of the modern improved makes of four 
valve engines there are two eccentrics, one for the 



VALVES AND VALVE SETTING 



159 



steam and the other for the exhaust valves. This 
arrangement permits of still greater latitude in adjust- 
ments for the economical use of steam. 

In Fig. 34 the piston is shown as just ready to begin 
the stroke towards the left. Admission is taking 
place at valve 2 and release at valve 3, valves 1 and 4 
being closed. The arrows show the direction in which 
the valves move. Motion is transmitted from the wrist 
plate to the valves by means of short connecting rods 
and cranks attached to the valve stems. These rods 



<s 






















l$k 


9 


/W""T 


//* 












1 ; 


B 




1 ®\ 
A V 

®1 


;J^2 


\c 




©1 


3 




^ 


F$ 






L * 


in iff 


d «f 


TWf-y 



FTGURE 35. 



are, or at least should be, fitted with right and left hand 
threads or turn buckles for the purpose of lengthening 
or shortening the rods while setting the valves. 

The valve gear of a corliss engine with a single 
eccentric is shown in Fig. 35. The connections of the 
exhaust valves with the wrist plate are positive, and 
the travel of these valves is fixed, being a constant 
quantity, but the connections of the steam valves with 
the wrist plate are detachable, being under the control 
of the governor. Various designs of releasing mechan- 



160 ENGINEERING 

ism are in use by different builders, but the same gen- 
eral principles govern the operation of all, viz., that 
the valve is quickly opened at the commencement of 
the stroke when the wrist plate has its fastest motion, 
and that the governor trips the releasing meehanism at 
that point in the stroke at which it is desired that cut 
off should take place, and that the valve is then 
quickly closed by means of a vacuum dash pot or, as in 
some types of engines, by a spring. Connection is 
made between the wrist plate and rocker arm by 
means of the hook rod, so-called because it hooks over 
the wrist plate pin, and can easily be disconnected in 
case it is desired to work the valves by hand, as in 
warming up the engine preparatory to starting up. 

Referring to Fig. 35, A is the wrist plate, B and C 
are the dash pot rods, D, D' the dash pots and H R the 
hook rod. G and G' represent the governor rods, and 
the figures 1, 2, 3 and 4 indicate the valve rods with 
turn buckles for changing their lengths. 

As in setting the slide valve, the first requisite in 
setting corliss valves is to put the engine on the cen- 
ter, the method of doing which has been fully 
described. Next adjust the length of the hook rod, if 
it is adjustable, if not, then the eccentric rod so that 
the wrist plate will vibrate equal distances each way 
from its central position which is marked on top of 
the hub. (See Fig. 36.) It will be noticed that there 
are four marks, A, B, C and D. Marks A and B are on 
the hub of the wrist plate and the stationary flange 
against which it turns, and when they are in line, indi- 
cate that the wrist plate is central. Marks C and D 
are on the stationary flange at equal distances each 
way from B, and when the engine is running mark A 
should travel to the right until it is in line with D and 



VALVES AND VALVE SETTING 



161 



to the left until in line with C, or it may happen that 
A will travel past C and D or perhaps not quite to 
them, but which ever it does, it should stop at equal 
distances from them. This adjustment should be care- 
fullv made before setting the valves, because if any 




FIGURE 36. 

change is made in the lengths of the eccentric rod or 
hook rod after the valves are once set it will seriously 
affect the action of all the valves. 

The method of adjusting the rocker arm so that it 
will vibrate correctly has been already described and 
it is very desirable that its travel should be equidistant- 



162 



ENGINEERING 



in either direction from a vertical position, but if it is 
found that the hook rod is non-adjustable as to length 
and that the wrist plate still vibrates too far in one 
direction, then the adjustment must be made on the 
length of the eccentric rod, which can be screwed into 
or out of the strap. The vibration of the wrist plate 
should then be tested by turning the eccentric around 
on the shaft in the direction the engine is to run. 
When this is found to be correct the next step is to 
remove the back bonnets from the valve chambers. 
Fig. 37 represents one of the steam valves and Fig. 38 



(0) 

/>> — 


: / 


'-■ \ 


: 


: ) 


* ( 


^ 



FIGURE 37. 



one of the exhaust valves, each with back bonnet 
removed, showing the ends of the valves. 

The working edges of the valves, as well as the 
ports of a corliss engine, cannot be seen when the 
valves are in place, owing to the fact that the circular 
ends of the valves fill the spaces at the ends of the 
valve chambers, but certain marks will be found on the 
ends of the valves, and corresponding marks on the 
faces of the chambers which serve as a guide in set- 
ting the valves. Referring to Fig. 37, mark V on the 
.end of the valve is in line with the edge of the valve, 
and P indicates the edge of the porr. The same let' 



VALVES AND VALVE SETTING 



163 



ters apply to Fig. 38. Having removed the bonnets 
and found the marks, temporarily secure the wrist 
plate in its central position by tightening one of the 
set screws on the eccentric. Then connect the valve 
rods, adjusting their lengths so that the steam valves 
will have from % to j\ in. lap, as in Fig. 37, and the 
exhaust valves from ^- 2 - to T 3 ¥ in. opening, as in Fig. 38. 
These figures vary according to the size of the engine, 
the smaller figures being for small size engines and the 
larger figures apply to large sizes. 

In adjusting the steam valves be sure and note the 




figure 38. 



direction in which they turn to open. In most corliss 
engines the arm of the crank to which the valve rod is 
connected extends downwards from the valve stem, 
as in Fig. 35. This will cause the valve to move 
towards the wrist plate in opening. After the valve 
rods have been properly adjusted as to length, place 
the engine on either center by the method previously 
explained and move the eccentric around on the shaft 
in the direction in which the engine is to run until it is 
far enough ahead of the crank to allow the steam 
valve the proper amount of lead opening, which will 
vary according to the size of the engine. Table 7 



164 



ENGINEERING 



gives the lap and lead for various sizes of corliss 
engines from 12 to 42 in. bore. Having tightened the 

TABLE 7. 



Size of Engine. 


Lap of Steam 
Valve. 


Lead Opening of 
Steam Valve. 


Lead Opening of 
Exhaust Valve. 


12 inches 


\ inch 


^ inch 


sh inch 


14 


5 " 
Te 


32 




3V " 


16 


5 < 1 


_1_ 




JL << 


T6 


16 




32 


18 


3 11 

8 


16 




A " 


20 " 


3 " 
8 


A 




¥ J 


22 " 


3 u 


ft 




1 1 6 


24 


r 7 e " 


3 
3"2 




3\ " 


26 


7 '< 

T6 


3 
32 




3 " 
32 


28 


r 7 e " 


3 
32 




ft •: 


30 


i " 


A 




I !! 


32 


i " 


#2 




1 


34 


1 '< 
2 


1 




1 " 


36 " 


fr " 


1 




1 << 

"S" 


38 " 


1% " 


i 




1 3 6 " 


40 


.ft " 


1 

8 




A " 


42 


T 9 6 " 


8 


r 3 e " 



eccentric set screws, turn the engine around, to the 
opposite center and note whether the lead is the same 
on each end. If there is a difference it can generally 
be equalized by slightly altering the length of one of 
the valve rods. The valves should also be adjusted 
by means of the indicator at the first opportunity, as 
that is the only absolutely correct method. 

The next point to receive attention is the adjustment 
of the lengths of the horizontal rods extending from 
the governor to the releasing mechanism, so that the 
steam valves will cut off at equal points in the stroke. 
This is done by raising the hook rod clear of the wrist 
plate pin, and with the bar provided for the purpose 
move the wrist plate to either one of its extreme posi- 
tions as shown by the marks on the hub (see Fig. 36) 



VALVES AND VALVE SETTING 165 

and holding it in this position adjust the length of the 
governor rod for the steam valve (which will then be 
wide open) so that the boss or roller which trips the 
releasing mechanism is just in contact, or within ^ in. 
of it. Then move the wrist plate to the other extreme 
of its travel and adjust the length of the other rod in 
the same manner. To prove the accuracy of the 
adjustment, raise the governor balls to their medium 
position, or about where they would be when the 
engine is running at its normal speed and block them 
there. Then having again connected the hook rod to 
the wrist plate, turn the engine around in the direction 
in which it is to run, and when the valve is released, 
measure the distance upon the guide that the crosshead 
has traveled from the end of the stroke. Now con- 
tinue to turn the engine in the same direction until the 
other valve is released, and measure the distance that 
the crosshead has traveled from the opposite end of 
the stroke, and if the cut off is equalized these two 
distances will be the same. If there is a difference, 
lengthen one rod and shorten the other until the point 
of cut off is the same for both ends. 

The lengths of the dash pot rods should also be 
adjusted so that when the plunger is at the bottom of 
the dash pot the valve lever will engage the hook. 

After all adjustments have been made tighten the 
lock nuts on all the rods. 

Questions 

i. What important features in the operation of an 
engine are dependent upon a correct adjustment of the 
valves? 

2. How many different types of valves are there in 
general use? 



166 ENGINEERING 

3. What are the basic principles governing the 
adjustment of the valves of an engine? 

4. Name two important functions of a valve. 

5. What is the effect of increasing the outside lap? 

6. What is the result of increasing the inside lap? 

7. What advantage has an engine of the four valve 
type over one with but a single valve? 

8. Suppose a valve had neither lap nor lead, what 
would be the position of the eccentric in relation to 
the crank? 

9. What is meant by the term "angular advance," 
and why is it necessary? 

10. What is the first function of the valve at the 
commencement of the stroke? 

11. What is the second function? 

12. What is the travel of a slide valve equivalent to? 

13. What is the third function of the valve? 

14. What is the fourth function? 

15. What will be the effect if a valve has no inside 
lap? 

16. How can the action of a slide valve be graphically 
illustrated? 

17. Name the two most commonly used valve dia- 
grams. 

18. What is meant by the expression, "radius of 
eccentricity"? (See Chapter VIII.) 

19. Why must a valve have outside lap? 

20. What is the object in giving a valve inside 
lap? 

21. What is the result of decreasing the angular 
advance? 

22. What will be the result if the travel of the valve 
is decreased? 

23. What three changes must be made in order to 



VALVES AND VALVE SETTING 167 

cause an earlier cut off in an engine that has a fixed 
cut off? 

24. What is the first step in the operation of valve 
setting? 

25. When is an engine on the dead center? 

26. What precautions should be observed in turning 
an engine to place it on the center? 

27. Why is this necessary? 

28. Describe briefly the process of placing an engine 
on the dead center. 

29. What is the next move in the routine of valve 
setting? 

30. What should be done with the valve before con- 
necting it to the valve rod? 

31. How may the outside lap be ascertained? 

32. How is the amount of inside lap found? 

33. Should the valve be rigidly secured to the stem? 

34. Describe the proper method of adjusting the 
length of the rod in order that the valve may travel 
correctly. 

35. How is the correct position of the eccentric on 
the shaft ascertained? 

36. If the lead is not the same at each end of the 
stroke, how may it be equalized? 

37. If there is more lead than is desired, how may it 
be decreased? 

38. What is the function of a shaft governor in rela- 
tion to the eccentric? 

39. Why is the four valve type of engine more eco- 
nomical in the use of steam than the single valve type 
with fixed cut off? 

40. How should the wrist plate be adjusted? 

41. If the wrist plate does not vibrate correctly what 
will be the result? 



168 ENGINEERING 

42. How should the rods connecting the governor 
with the releasing mechanism be adjusted? 

43. How may this adjustment be tested? 

44. How should the dash pot rods be adjusted as to 
length? 



CHAPTER VII 

THE INDICATOR 

The indicator — Its invention and improvement — Principles 
governing its operation — Diagrams from condensing and non- 
condensing engines — Sizes of springs to be used for various 
pressure — Reducing mechanism — The reducing wheel — 
Different forms of pendulum reducing motion — Brumbo pul- 
ley — The pantograph — Attaching the indicator — Parts of the 
cylinder to which indicator pipes should not be connected — 
Care of the insirument — Cleaning, oiling, etc. — Directions for 
taking diagrams. 

The Indicator. One of the greatest aids to the eco- 
nomical operation of the steam engine is the indicator, 
and it is the privilege of every engineer to have at least 
an elementary, if not a thorough knowledge of its prin- 
ciples and working. The time devoted to the study of 
the indicator, and in its application to the engine, is 
time well spent, and in the end will well repay the 
student of steam engineering. 

Inve?itor. The indicator was invented and first ap- 
plied to the steam engine by James Watt, whose restless 
genius was not satisfied with a mere outside view of his 
engine as it was running, but he desired to know more 
about the action of the steam in the cylinder, its pressure 
at different portions of the stroke, the laws governing its 
expansion after being cut off, etc. Watt's indicator, 
although crude in its design and construction, con- 
tained embodied within it all of the principles of the 
modern instrument. 

Principles. These principles are: 

First. The pressure of the steam in the engine 
- 169 



170 



ENGINEERING 



cylinder throughout an entire revolution, against a 
small piston in the cylinder of the indicator, which in 
turn is controlled or resisted in its movement by a 




SECTIONAL VIEW CROSBY INDICATOR. 



spring of known tension, so as to confine the stroke of 
the indicator piston within a certain small limit. 

Second. The stroke of the indicator piston is com- 
municated by a multiplying mechanism of levers and 
parallel motion to a pencil moving in a straight line. 
The distance through which the pencil moves being 



THE INDICATOR 



171 



governed by the pressure in the engine cylinder and 
the tension of the spring. 

Third. By the intervention of a reducing mechan- 
ism and a strong cord, the motion of the piston of the 
engine throughout an entire revolution is communi- 
cated to a small drum attached to and 
forming a part of the indicator. The 
movement of the drum is rotative and 
in a direction at right angles to the 
movement of the pencil. The forward 
stroke of the engine piston causes the 
drum to rotate through part of a revo- 
lution and at the same time a clock 
spring connected within the drum is 
wound up. On the return stroke the 
motion of the drum is reversed and the 
tension of the spring returns the drum 
to its original position and also keeps 
the cord taut. 

To the outside of the drum a piece of 
blank paper of suitable size is attached and held in place 
by two clips. Upon this paper the pencil in its motion 
up and down traces a complete diagram of the pressures 
and other interesting events transpiring within the en- 
gine cylinder during the revolution of the engine. In 
fact the diagram traced upon the paper is the compound 
result of two concurrent movements. First, that of the 
pencil caused by the pressure of the steam against 
the indicator piston; second, that of the paper drum 
caused by, and coincident with, the motion of the 
engine piston. The upper end of the indicator cylin- 
der is always open to the atmosphere, the steam acting 
only upon the underside of the small piston, and when 
the cock connecting the cylinders of the engine and 




CROSBY INDI- 
CATOR SPRING. 



172 ENGINEERING 

indicator is closed, both ends of the indicator cylinder 
are open to atmospheric pressure, and the pencil then 
stands at its neutral position. If now the pencil is 
held against the paper and the drum rotated either by 
hand or by connecting it with the cord, a horizontal 
line will be traced. - This line is called the atmospheric 
line, meaning the line of atmospheric pressure, and it 
is a very important factor in the study of the diagram. 

If the engine is a non-condensing engine the pencil 
in tracing the diagram will, or at least, should not fall 
below- the atmospheric line at any point, but will on 
the return stroke trace a line called the line of back 
pressure at a distance more or less above the atmos- 
pheric line and very nearly parallel with it. If the 
engine is a condensing engine the pencil will drop 
below the atmospheric line while tracing the line of 
back pressure on the diagram, and the distance this 
line is below the atmospheric line will depend upon 
the number of inches of vacuum in the condenser. 

As before stated, the length of stroke of the indi- 
cator piston and the pencil movement as well is 
controlled by a spiral steel spring which acts in resist- 
ance to the pressure of the steam. These springs are 
made of different tensions in order to be suitable to 
different steam pressures and speeds, and are numbered 
20, 40, 60, etc., the number meaning that a pressure per 
square inch in the engine cylinder corresponding to the 
number on the spring will cause a vertical movement of 
the pencil through a distance of one inch. Thus, if a 
number 20 spring is used and the pressure in the 
cylinder at the commencement of the stroke is 20 lbs. 
per square inch, the pencil will be raised one inch, or 
if the pressure is 30 lbs., the pencil will travel 1^ in., 
and if there is a vacuum of 20 in. in the condenser, 



THE INDICATOR 



ra 



the pencil will drop y% in. below the atmospheric line 
for the reason that 20 in. of vacuum corresponds to a 




IMPROVED TABOR INDICATOR WITH OUTSIDE CONNECTED SPRING. 
A.SHCROFT MFG. CO., N. Y. 



pressure of about. 10 lbs. less than atmospheric pressure 
or an absolute pressure of about 4 lbs. If a 60 spring 
is used a pressure of 60 lbs. in the engine cylinder will 



174 



ENGINEERING 



be required to raise the pencil one inch, or 90 lbs. to 
raise it \y 2 in. 

The Ashcroft Manufacturing Co. of New York, 
makers of the well known Tabor indicator, have 
recently introduced a new feature in indicator work by- 
connecting the spring on top of the cylinder and in 
plain view of the operator. This arrangement removes 
the spring from the influence of direct contact with the 





figure 40. 



steam, and it is subject only to the temperature of the 
surrounding atmosphere. It is claimed that as a result 
of this the accuracy of the spring is insured and that 
no allowance need to be made in its manufacture for 
expansion caused by the high temperature to which it 
is subject when located within the cylinder. Another 
good feature of this design is, that the spring can be 
easily removed without disconnecting any one part of 
the instrument in case it is desired to change springs. 



THE INDICATOR 



175 



A cut of the improved instrument is herewith pre- 
sented. 

Fig. 39 is a sectional view of the American Thomp- 
son improved indicator. Fig. 40 shows the spring. 
Fig. 41 is a three way cock for attaching the indicator 
to thecylinder. 

Reducing Mechanism. Probably the only practically 
universal mechanism for reducing the motion of the 
crosshead is the reducing wheel, a device in which, by 




FIGURE 41. 



the employment of gears and pulleys of different diam- 
eters, the motion is reduced to within the compass of 
the drum, and the device is applicable to almost any 
make of engine, whether of high or low speed. Some 
makers of indicators attach the reducing wheel directly 
to the indicator, thus producing a neat and very con- 
venient arrangement. Fig. 42 shows the indicator 
complete with reducing wheel attached. 

One of the most accurate and easily applied devices 
for reducing the motion of the piston is the wooden 



176 



ENGINEERING 



pendulum in its various forms. (See Figs. 43, 44 and 
45.) It consists of a flat strip of pine or other light 
wood of a length net les , than one ard a half times the 
stroke of the engine, a:id if made longer it will be 
better. It should be from % to ]/b in. thick and have 
an average width of abjut4in. If the engine to be 




FIGURE 42. 



indicated is horizontal the bar or pendulum is to be 
pivoted at a fixed point directly above and in line with 
the side of the crosshead, as that is generally the most 
convenient point of attachment. The pivot can be 
fixed to a permanent standard bolted to the frame of 
the engine (Fig. 46), or it may be secured to the ceil- 



THE INDICATOR 



177 



ing of the room or even to a post fastened to the floor. 
It the engine is vertical the bar can be pivoted to the 
wall of the room or a strong post firmly secured to the 
floor. The .connection with the crosshead is best 
accomplished by means of a short bar or link. A con- 
venient length for this bar is one-half the stroke of the 
engine. To locate the correct point for the pivot, 





figure 43. 



assuming the length of the short bar to be one-half the 
length of the stroke, proceed as follows: 

Place the engine on the center with the crosshead at 
the end of the stroke towards the crank. Then having 
previously bored a hole for the pivot in one end of the 
pendulum bar and in the other end a hole for connect- 
ing with the link, suspend the pendulum by a tem- 
porary pin, as a large wood screw, directly above and in 



178 



ENGINEERING 



line with the stud or bolt hole which has previously 
been tapped into the crosshead at any convenient 
point. The pendulum should be temporarily sus- 
pended at such a height that when it hangs perpendic- 
ular the hole in its lower end will line up accurately 
with the hole or stud in the crosshead. Now swing 
the pendulum in either direction a distance equal to 
the length of the link (one-half the stroke of the 




FIGURE 44. 



engine) from the crosshead connection and note the 
distance that the bottom hole is above a straight edge 
laid horizontal and in line with the center of the stud 
in the crosshead. This will give the total vibration of the 
free end of the link from a line parallel with the line 
of the engine and the permanent location of the pivot 
should be one-half of this distance below the tem- 
porary point of suspension. This will allow the link 



THE INDICATOR 



179 



to vibrate equally above and below the center of its 
connection with the crosshead. Fig. 47 shows a com- 
plete connection of this character. 

Sometimes the end is slotted and thus directly con- 
nected to the stud in the crosshead, dispensing with 
the link. In this case it is necessary to locate the 
pivot at a point perpendicular to the center of travel 
of the stud in the crosshead. (See Fig. 43.) The link 





FIGURE 45. 



connection is to be preferred, however. The cord can 
be attached to the pendulum at a point near the pivot 
which will give the desired length of diagram. This 
point can be determined by multiplying the length of 
the pendulum by the desired length of diagram and 
dividing the product by the stroke. For convenience 
these terms should be expressed in inches. Thus, 
assume stroke of engine to be 48 in., length of pendu- 



180 



ENGINEERING 



lum \y 2 times length of stroke = 72 in. Desired length 
of diagram 3 in. Then 72 x 3 -5- 48 = 4.5 in., which is 




figure 46. 

the distance from center of pivot to point of connec- 
tion for the cord. This can be either a small hofe 




FIGURE 47. 



THE INDICATOR 



181 



bored through the pendulum or a wood screw to which 
the ccrd can be attached. From this point the cord 
should be led over a guide pulley located at such 
height that when the pendulum is vertical the cord 
will leave it at right angles. After leaving the guide 
pulley the cord can be carried at any angle desired. 
The Brumbo Pulley. Another method of connecting 
the cord to the pendulum is to run the cord over a 
grooved segment, called a Brumbo pulley, connected 




FIGURE 48. 



with the pivoted end of the pendulum (Fig. 48), but 
with this arrangement, owing to the curved travel of 
the pendulum, there is greater liability to distortion of 
the diagram than in the first method. In case it is 
desired to use the Brumbo pulley, the radius of the 
segment can be found by the same process as that 
used for finding the point for connecting the cord 
directly to the pendulum. 

One of the neatest and most easily applied devices 



182 



ENGINEERING 



for reducing the motion of the crosshead is the panto- 
graph. (See Fig. 49.) No dimensions are essential 
except that it shall be made reasonably strong of some 
light, tough variety of wood, and that the pins and 
holes be nicely fitted to each other so that while the 
movement may be free there shall at the same time 
not be too much lost motion. The pantograph should 
be of such capacity that it will just close up nicely 
when the engine is at mid stroke and open out nicely 
when at its extreme travel. The two ends, C and D, 




figure 49. 



are each to be fitted with a pin extending through far 
enough so that pin C can be hooked into a hole or 
socket on the crosshead, while pin D rests in a socket 
in the top of a post secured to the floor at a 
point opposite the center of travel of the crosshead 
and of such height as will allow the pantograph to lie 
in a horizontal position. Also the distance of the post 
from the guides must be adjusted so as to allow the • 
device to close up at mid stroke and open out at full 
stroke without any straining of the parts. The point 
F of connection for the cord will always have a motion 



THE INDICATOR 



183 



parallel with, and simultaneous with, that of the cross- 
head; the pin to which the cord is attached can be set 
in any one of the holes that will give the desired 
length for the diagram. The motion given by this 
device is accurate, although it may become necessary 




CROSBY REDUCING WHEEL. 



in some cases, especially with long stroke engines, to 
introduce a guide pulley to carry the cord from the 
pantograph. 

Attaching the Indicator. The cylinders of most 
engines at the present time are drilled and tapped for 



184 ENGINEERING 

indicator connections before they leave the shop, 
which is eminently proper, as no engine builder, or 
purchaser either, should be satisfied with the perform- 
ance of a new engine until after it has been accurately, 
tested and adjusted with the indicator. 

The main requirements in these connections are that 
the holes shall not be drilled near the bottom of the 
cylinder where water is likely to find its way into the 
pipes, neither should they be in a location where 
the inrush of steam from the ports will strike them 
directly, nor where the edge of the piston is liable to 
partly cover them when at its extreme travel. An 
engineer before he undertakes to indicate an engine 
should satisfy himself that all these requirements are 
fulfilled. Otherwise he is not likely to' obtain a true 
diagram. The cock supplied with the indicator is 
threaded for one-half inch pipe and unless the engine 
has a very long stroke it is the practice to bring the 
two end connections together at the side or top of the 
cylinder and at or near the middle of its length, where 
they can be connected to a three way cock. The pipe 
connections should be as short and as free from elbows 
as possible in order that the steam may strike the 
indicator piston as nearly as possible at the same 
moment that it acts upon the engine piston. 

The work of taking diagrams is very much simplified 
by having both ends of the cylinder connected to one 
common tee or a three way cock as above described, 
but for long stroke engines there should be two indi- 
cators, one for each end and the diagrams should be 
taken simultaneously if it is desired to adjust the 
valves by the indicator. In this case an assistant 
would be required to manipulate one of the instru- 
ments. 



TTTE INDICATOR 185 

The pipes should always be thoroughly blown out 
by allowing- the steam to blow through the open cock 
during several revolutions of the engine, before con- 
necting the indicator. If this is not done there is a 
moral certainty that grit and dirt will get into the 
cylinder of the indicator, where the pressure of the 
least atom of grit will cause the delicate instrument to 
work badly. 

Selecting a Spring. The proper number of spring to 
use depends upon the boiler pressure in the case of an 
automatic cut off engine, but for an engine with a 
fixed cut off and throttling governor the number of the 
spring to be selected will depend upon the initial 
pressure in the cylinder. A convenient rule is to 
select a spring numbered one-half as high as the pres- 
sure; for instance, if the boiler pressure is 80 lbs., use a 
No. 40 spring, which will give a diagram 2 in. in height. 

Care of the Instrument. The indicator should be 
cleaned and oiled both before and after using. The 
best material for wiping it is a clean piece of old soft 
muslin of fine texture, as there is not so much liability 
of lint sticking to or getting into the small joints. Use 
good clock oil for the joints and springs, and before 
taking diagrams it is a good practice to rub a small 
portion of cylinder oil on the piston and the inside of 
the cylinder, but when about to put the instrument 
away these should be oiled with clock oil also. None 
but the best cord should be used for connecting the 
paper drum with the reducing motion, as a cord that is 
liable to stretch will cause trouble. Suitable cord and 
also blank diagrams can generally be secured from 
firms manufacturing and selling indicators. After the 
indicator has been screwed on to the cock connecting 
with the pipe, the cord must be adjusted to the proper 



180 ENGINEERING 

length before hooking it on to the drum. This must 
be done while the engine is running, by taking hold 
of the loop on the cord connected with the reducing 
motion with one hand, and with the other hand grasp 
the hook on the short cord attached to the drum, then 
by holding the two ends near each other during a revo- 
lution or two it will be seen whether the long cord 
needs to be shortened or lengthened. 

The length of the diagram is determined by the 
point of connection of the cord to the pendulum as has 
been heretofore explained. Care should be exercised 
in placing the paper on the drum to see that it is 
stretched tight and firmly held by the clips. The 
pencil point having been first sharpened by rubbing it 
on a piece of fine emery cloth or sand paper should be 
adjusted by means of the pencil stop with which all 
indicators should be provided, so that it will have just 
sufficient bearing against the paper to make a fine, 
plain mark. If the pencil bears too hard on the paper 
it will cause unnecessary friction and the diagram will 
be distorted. The best method of ascertaining this 
fact and also whether the travel of the drum is equally 
divided between the stops, is to place a blank diagram 
on the drum, connect the cord and while the engine 
makes a revolution hold the pencil against the paper. 
Then unhook the cord, remove the paper and if the 
travel of the drum is not divided correctly it can be 
changed. 

Having thus arranged all the preliminary details, 
place a fresh blank on the drum, being careful to keep 
the pencil out of contact with it, connect the cord, 
open the cock admitting steam to the indicator and 
after the pencil has made a few strokes to allow the 
cylinder to become warmed up, then gently swing it 



THE INDICATOR 187 

around to the paper drum and hold it there while the 
engine makes a complete revolution. Then move the 
pencil clear of the paper, close the cock and unhook 
the cord. Now trace the atmospheric line by holding 
the pencil against the paper while the drum is revolved 
by hand. This method of tracing the atmospheric line 
is preferable to that of tracing it immediately after 
closing the cock and while the drum is still being 
moved by the engine, for the reason that there is not 
so much liability of getting the atmospheric line too 
high owing to the presence of a slight pressure of 
steam remaining under the indicator piston for a 
second or two just after closing the cock; also the line 
drawn by hand will be longer than one drawn while 
the drum is moved by the motion of the engine and 
will therefore be more readily distinguished from the 
line of back pressure. 

Having secured a truthful diagram, it now remains 
to take as many as are desired, and if the object is to 
set the valves of the engine, the diagrams from each 
end of the cylinder should follow each other as quickly 
as possible in order that the conditions of load and 
steam pressure may be the same. When the indicator 
is connected so that diagrams can be taken from both 
ends without changing it, the above conditions can 
generally be realized. But if diagrams can only be 
taken from one end at a time, the only way to arrive 
at correct conclusions in relation to the adjustment of 
the valves will be to see that the boiler pressure is 
practically the same at the time of taking diagrams 
from either end and that the position of the governor 
is also the same, assuming that the load on the engine 
is practically constant. This applies of course to an 
automatic cut off. 



188 ENGINEERING 

As soon as the diagrams are taken the following 
data should be noted upon them: The end of the 
cylinder, whether head or crank; boiler pressure; and 
time when taken. Other data can be added after- 
wards. If the engine is an automatic cut off of the 
corliss type and the point of cut off on one end does 
not coincide with the other, the difference can gener- 
ally be adjusted while the engine is running by chang- 
ing the length of the rods extending from the governor 
to the tripping device. These rods are, or should be, 
fitted with right and left threads on the ends for this 
purpose. Any changes in the valves, such as giving 
them more lead, compression, etc., and which neces- 
sitates changing the length of the reach rods connect- 
ing them with the wrist plate, will have to be made 
while the engine is stopped, although with slow speed 
engines and the exercise of caution it is possible to 
make alterations in these rods while the engine is 
running. 

Questions 

1. What instrument is a necessary part of an 
engineers outfit? 

2. Who invented the indicator? 

3. Name the principles governing the action of the 
• indicator. 

4. What will a truthful diagram from a steam 
cylinder show? 

5. Does the steam act upon both sides of the indi- 
cator piston? 

6. What does the atmospheric line show? 

7. Is this line important in the study of the dia- 
gram ? 

8. Where should the line of back pressure appear in 
a diagram from a non-condensing engine? 



THE INDICATOR 189 

9. Where will the line of back pressure appear on a 
diagram from a condensing engine? 

10. What controls the length of stroke of the indi- 
cator piston? 

11. What does the number on the spring mean? 

12. What is one of the most convenient appliances 
for reducing the motion of the crosshead within the 
compass of the drum? 

13. What other appliances besides the reducing 
wheel may be employed for this purpose? 

14. What is a Brumbo pulley? 

15. What are the main requirements in indicator 
connections? 

16. What should be done with the pipes before 
attaching the indicator? 

17. Upon what does the selection of the scale of 
spring depend? 

18. What is a convenient rule to be observed in the 
selection of a spring? 

19. What is the best method of tracing the atmos- 
pheric line? 

20. What data should be noted on the diagram as 
soon as it is taken? 



CHAPTER VIII 

DEFINITIONS AND TABLES 

Definition of words, terms and phrases — Table of hyperbolic 
logarithms — Table of areas and circumferences of circles. 

In order to facilitate the study and analysis of indi- 
cator diagrams, the following definitions of technical 
terms, some of which have already been explained in 
another part of this book, are here given. 

Absolute pressure. Pressure reckoned from a perfect 
vacuum. It equals the boiler pressure plus the atmos- 
pheric pressure. 

Boiler pressure or gauge pressure. Pressure above the 
atmospheric pressure as shown by the steam gauge. 

Initial pressure. Pressure in the cylinder at the be- 
ginning of the stroke. 

Terminal pressure (T. P.). The pressure that would 
exist in the cylinder at the end of the stroke provided 
the exhaust valve did not open until the stroke was 
entirely completed. It may be graphically illustrated 
on the diagram by extending the expansion curve by 
hand to the end of the stroke. It is found theoretically 
by dividing the pressure at point of cut off by the ratio 
of expansion. Thus, absolute pressure at cut off = ioo 
lbs., ratio of expansion = 5; then 100 + 5 = 20 lbs., abso- 
lute terminal pressure. 

Mean effective pressure (M. E. P.). The average 
pressure acting upon the piston throughout the stroke 
minus the back pressure. 

Back pressure. Pressure which tends to retard the 
forward stroke of the piston. Indicated on the dia- 
gram from a non-condensing engine by the height of 
190 



DEFINITIONS AND TABLES 191 

HjC back pressure line above the atmospheric line. In 
a condensing engine the degree of back pressure is 
shown by the height of the back pressure line above 
an imaginary line representing the pressure in the 
condenser corresponding to the degree of vacuum in 
inches, as shown by the vacuum gauge. 

Total or absolute back pressure, in either a condensing 
or non-condensing engine, is that indicated on the 
diagram by the height of the line of back pressure 
above the line of perfect vacuum. 

Ratio of expansion. The proportion that the volume 
of steam in the cylinder at point of release bears to 
the volume at cut off. Thus, if the point of cut off is 
at one-fifth of the stroke, and release does not take 
place until the end of the stroke, the ratio of expan- 
sion, or in other words, the number of expansions, is 
5. When the T. P. is known the ratio of expansion 
may be found by dividing the initial pressure by 
the T. P. 

Wire drawing. When through insufficiency of valve 
opening, contracted ports, or throttling governor, the 
steam is prevented from following up the piston at full 
initial pressure until the point of cut off is reached, it 
is said to be wire drawn. It is indicated on the dia- 
gram by a gradual inclination downwards of the steam 
line from the admission line to the point of cut off. 
Too small a steam pipe from boiler to engine will also 
cause wire drawing and fall of pressure. 

Conde?iser pressure may be defined as the pressure 
existing in the condenser of an engine, caused by the 
lack of a perfect vacuum. As, for instance, with a 
vacuum of 25 in. there will still remain the pressure 
due to the 5 in. which is lacking. This will be about 
2.5 lbs. 



VM ENGINEERING 

Vacuum. That condition existing within a closed 
vessel from which all matter, including air, has been 
expelled. It is measured by inches in a column of 
mercury contained within a glass tube a little over 30 
in. in height, having its lower end open and immersed 
in a small open vessel filled with mercury. The upper 
end of the glass tube is connected with the vessel in 
which the vacuum is to be produced. When no 
vacuum exists the mercury will leave the tube and fill 
the lower vessel. When a vacuum is maintained in 
the condenser, or other vessel, the mercury will rise in 
the glass tube to a height corresponding to the degree 
of vacuum. If the mercury rises to the height of 30 
in. it indicates a perfect vacuum, which means the 
absence of all pressure within the vessel, but this con- 
dition is never realized in practice; the nearest 
approach to it being about 28 in. 

For purposes of convenience the mercurial vacuum 
gauge is not generally used, it having been replaced 
by the Bourdon spring gauge, although the mercury 
gauge is used for testing. 

The vacuum in a condenser is generally maintained 
by an air pump, although it can be produced and 
maintained by the mere condensation of the steam as 
it enters the condenser by allowing a spray of cold 
water to strike it. The steam when it first enters the 
condenser drives out the air and the vessel is filled 
with steam which, when condensed, occupies about 
1,600 times less space than it did before being con- 
densed, hence a partial vacuum is produced. 

While the vacuum in a condenser cannot be consid- 
ered as power at all, yet it occupies the anomalous 
position of increasing, by its presence, the capacity of 
the engine for doing work. This is owing to the fact 



DEFINITIONS AND TABLES 193 

that the atmospheric pressure or resistance which is 
always ahead of the piston in a non-condensing engine 
is, in the case of a condensing engine, removed to a 
degree corresponding to the height of the vacuum, thus 
making available just so much more of the pressure 
behind the piston. Thus, if the average steam pres- 
sure throughout the stroke is 30 lbs. and there is a 
vacuum of 26 in. maintained in the condenser, there 
will be 13 lbs. of resistance per square inch removed 
from in front of the piston, thus making available 
30+ 13 = 43 lbs. pressure per square inch. 

Absolute zero has been fixed by calculation at 461. 2° 
below the zero of the Fahrenheit scale. 

Piston displacement. The space or volume swept 
through by the piston in a single stroke. Found by 
multiplying thearea of piston by length of stroke. 

Piston clearance. The distance between the piston 
and cylinder head when the piston is at the end of the 
stroke. 

Steam clearance, ordinarily termed clearance. The 
space between the piston at the end of the stroke and 
the valve face. It is reckoned in per cent, of the total 
- piston displacement. 

Horse power (H. P.). 33,000 pounds raised one foot 
high in one minute of time. 

Indicated horse power {I. H. P.). The horse power 
as shown by the indicator diagram. It is found as 
follows: 

Area of piston in square inches x M. E. P. x piston 
speed in feet- 33,000. 

Piston speed. The distance in feet traveled by the 
piston in one minute. It is the product of twice the 
length of stroke expressed in feet multiplied by the 
number of revolutions per minute. 



104 ENGINEERING 

R. P. M. Revolutions per minute. 

Net horse pozver. I. H. P. minus the friction of the 
engine. 

Compressio?i. The action of the piston as it nears the 
end of the stroke, in reducing the volume and raising 
the pressure of the steam retained in the cylinder 
ahead of the piston by the closing of the exhaust 
valve. 

Boyle's or Mariotte s law of expanding gases. "The 
pressure of a gas at a constant temperature varies 
inversely as the space it occupies." Thus, if a given 
volume of gas is confined at a pressure of 50 lbs. per 
square inch and it is allowed to expand to twice its 
volume, the pressure will fall to 25 lbs. per square inch. 

Adiabatic curve. A curve representing the expansion 
of a gas which loses no heat while expanding. Some- 
times called the curve of no transmission. 

Isothermal curve. A curve representing the expan- 
sion of a gas having a constant temperature but 
partially influenced by moisture, causing a variation in 
pressure according to the degree of moisture or satura- 
tion. It is also called the theoretical expansion 
curve. 

Expansion curve. The curve traced upon the dia- 
gram by the indicator pencil showing the actual 
expansion of the steam in the cylinder. 

First law of thermody?iamics. Heat and mechanical 
energy are mutually convertible. 

Power. The rate of doing work, or the number of 
foot pounds exerted in a given time. 

Unit of work. The foot pound, or the raising of one 
pound weight one foot high. 

First law of motion. All bodies continue either in a 
state of rest or of uniform motion in a straight line, 



DEFINITIONS AND TABLES 195 

except in so far as they may be compelled by 
impressed forces to change that state. 

Work. Mechanical force or pressure cannot be con- 
sidered as work unless it is exerted upon a body and 
causes that body to move through space. The product 
of the pressure multiplied by the distance passed 
through and the time thus occupied is work. 

Momentum. Force possessed by bodies in motion, 
or the product of mass and density. 

Dynamics. The science of moving powers or of 
matter in motion, or of the motion of bodies that 
mutually act upon each other. 

Force. That which alters the motion of a body, or 
puts in motion a body that was at rest. 

Maximum theoretical duty of steam is the product of 
the mechanical equivalent of heat, viz., 778 ft. lbs. 
multiplied by the total heat units in a pound of steam. 
Thus, in one pound of steam at 212 reckoned from 32 
the total heat equals 1,146.6 heat units. Then 
778 x 1,146.6 equals 892,054.8 ft. lbs. = maximum duty. 

Steam efficiency may be expressed as follows: 

Heat converted into useful work . . „ . 

i =^ : — = and maximum effic- 

Heat expended 

iency can only be attained by using steam at 

as high an initial pressure as is consistent with safety 

and at as large a ratio of expansion as possible. The 

percentage of efficiency of steam used at atmospheric 

pressure in a non-expansive engine is very low; as, for 

instance, the heat expended in the evaporation of one 

pound of water at 32 into steam at atmospheric 

pressure = 1,146.6 heat units, and the volume of steam 

so generated = 26.36 cu. ft. 

One cubic foot of steam at 212 contains energy 

equal to 144x14.7 = 2,116,8 ft. lbs., and 26.36 cu. 



196 ENGINEERING 

ft. = 2, 1 16.8 x 26.36 = 55,798.84 ft. lbs., which divided by 
the mechanical equivalent of heat, viz., 778 ft. 
lbs. = 71.72 heat units, available for useful work. The 
per cent, of efficiency therefore is 71 fi46 6°° = 6.28 per 
cent. But suppose the initial pressure to have been 
200 lbs. absolute, and that the steam is allowed to 
expand to thirty times its original volume. The heat 
expended in evaporating a pound of water at 32 into 
steam at 200 lbs. absolute pressure = 1,198.3 heat units, 
and the volume of steam so generated = 2.27 cu. ft. 
The average pressure during expansion would be 29.34 
lbs. per square inch and the volume when expanded 
thirty times would equal 2.27 x 30 = 68. 1 cu. ft. 

One cubic foot of steam at 29.34 lbs. pressure equals 
144 x 29.34 = 4,224.96 ft. lbs., and 68. 1 cu. ft. will equal 
4224.96x68.1=287,719.7 ft. lbs. of energy, which 
divided by the equivalent, 778, equals 370.2 heat units, 
and the per cent, of efficiency will be 37 ^ 9 g 3 10 ° = 30.8 
per cent. 

Engine efficiency. If the engine is considered merely 

as a machine for converting into useful work the heat 

energy in the steam regardless of the cost of fuel, its 

efficiency may be expressed as follows: 

Heat converted into useful work 

Total heat received in the steam 

Example. Assume an engine to be receiving steam 
at 95 lbs. absolute pressure, that the consumption of 
dry steam per horse power per hour equals 20 lbs., that 
the friction of the engine amounts to 15 per cent., and 
that the temperature of the feed water is raised from 
6o° to 170 by utilizing a portion of the exhaust. 

In a pound of steam at 95 lbs. absolute there are 
1,180.7 heat units, and in a pound of water at 170 there 



DEFINITIONS AND TABLES 197 

are 138.6 units of heat, but 28.01 of these heat units 
were in the water at its initial temperature of 6o°. 
Therefore the total heat added to the water by the 
exhaust steam equals 138.6 -28.01 = no. 59 heat units, 
and the total heat in each pound of steam to be 
charged up. to the engine is 1,180.7 - 1 10.59 = 1,070. 1 1, 
and the total for each horse power developed per hour 
will be 1,070. n x 20 - 21,402.2 heat units. 

A horse power equals 33,000 ft. lbs. per minute, or 
sixty times 33,000 = 1,980,000 ft. lbs. per hour. From 
this must be deducted 15 per cent, for friction of the 
engine, leaving 1,683,000 ft. lbs. for useful work. 
Dividing this by the equivalent, viz., 778 ft. lbs., 
gives 2,163.2 heat units as the heat converted into one 
horse power of work in one hour, and the percentage 

of efficiency of the engine will be ^f^l™ = iai P er 
cent. 

Efficiency of the plant as a whole includes boiler and 
engine efficiency and is to be figured upon the basis of 
Heat converted into useful work 
Calorific or heat value of fuel 

Horse power constant of an engine is found by multi- 
plying the area of the piston in square inches by the 
speed of the piston in feet per minute and dividing the 
product by 33,000. It is the power the engine would 
develop with one pound mean effective pressure. To 
find the horse power of the engine, multiply the M. 
E. P. of the diagram by this constant. 

Logarithms. A series of numbers having a certain 
relation to the series of natural numbers, by means of 
which many arithmetical operations are made com- 
paratively easy. The nature of the relation will be 
understood by considering two simple series, such as 
the following, one proceeding from unity in geomet- 



198 ENGINEERING 

rical progression and the other from o in arithmetical 
progression: 

Geom. series, I, 2, 4, 8, 16, 32, 64, 128, 256, 512, etc. 

Arith. series, o, 1, 2, 3, 4, 5, 6, 7, 8, 9, etc. 

Here the ratio of the geometrical series is 2 and any 
term in the arithmetical series expresses how often 2 
has been multiplied into 1 to produce the correspond- 
ing term of the geometrical series. Thus, in proceeding 
from 1 to 32 there have been 5 steps or multiplications 
by the ratio 2; in other words, the ratio of 32 to 1 is 
compounded 5 times of the ratio of 2 to 1. The above 
is the basic principle upon which common logarithms 
are computed. 

Hyperbolic logarithms. Used in figuring the M. E. P. 
of a diagram from the ratio of expansion and the 
initial pressure. Thus, hyperbolic logarithm of ratio 
of expansion -f 1 multiplied by absolute initial pres- 
sure and divided by ratio of expansion = mean forward 
pressure. From this deduct total back pressure and 
the remainder will be mean effective pressure. The 
hyperbolic logarithm is found by multiplying the com- 
mon logarithm by the constant 2.302585. Table 8 
gives the hyperbolic logarithms of numbers usually 
required in calculations of the above nature. 

Steam co?isnmption per horse power per hour. The 
weight in pounds of steam exhausted into the atmos- 
phere or into the condenser in one hour divided by the 
horse power developed. It is determined from the 
diagram by selecting a point in the expansion curve 
just previous to the opening of the exhaust valve and 
measuring the absolute pressure at that point. Then 
the piston displacement up to the point selected, plus 
the clearance space, expressed in cubic feet, will give 
the volume of steam in the cylinder, which multiplied 



DEFINITIONS AND TABLES 



199 



Table 8. 

Hyperbolic Logarithms. 



No. 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


I.OI 


. OO99 


3.00 


1 .0986 


5.00 


I . 6094 


7.0c 


1-9459 


9.00 


2. 1972 


i 05 


O.0487 


3.05 


1. 1151 


5.05 


1 .6194 


7.05 


I.9530 


9-05 


2.2028 


1 . 10 


0.0953 


3- 10 


I.I34I 


5-IO 


1.6292 


7.IC 


I .9600 


9. 10 


2.2083 


1. 15 


0.1397 


3.15 


1. 1474 


5.15 


I . 6390 


7.15 


I. 967 1 


9-15 


2.2137 


1.20 


0.1823 


3.20 


1 .1631 


5.20 


I.6486 


7 .2C 


I . 9740 


9.20 


2.2192 


1.25 


0.2231 


3-25 


1. 1786 


5.25 


I.6582 


7.25 


I .9810 


9.25 


2.2246 


1.30 


0.2623 


3.30 


1. 1939 


5.30 


I.6677 


7.30 


L9879 


9.3o 


2.23IO 


i-35 


0.3001 


3-35 


1 .2090 


5-35 


I. 6771 


7.35 


L9947 


9-35 


2.2354 


1.40 


O.3364 


3.40 


1.2238 


5.40 


I.6864 


7.4c 


2 . OOI 5 


9.40 


2 . 2407 


1-45 


0.37I5 


3-45 


I.2384 


5-45 


I.6956 


7.45 


2.00I8 


9-45 


2 . 2460 


1.50 


O.4054 


3.50 


I.2527 


5.50 


I . 7047 


7.50 


2.OI49 


9 -5o 


2.2513 


1.55 


0.4382 


3-55 


I.2669 


5-55 


I. 7138 


7.55 


2.02I5 


9-55 


2.2565 


1.60 


O.4700 


3.6o 


1.2809 


5.60 


I.7228 


7.60 


2.028I 


9.60 


2.26l8 


1.65 


0.5007 


3.65 


1.2947 


5.65 


I. 7316 


7.65 


2.0347 


9-65 


2.267O 


1.70 


0. 5306 


3 -7o 


1.3083 


5.7o 


I • 7405 


7.70 


2.0412 


9.70 


2.2721 


1-75 


0.5596 


3-75 


I. 3217 


5-75 


I. 7491 


7.75 


2.0477 


9-75 


2.2773 


1.80 


0.5877 


3.80 


1.3350 


5.80 


1.7578 


7.80 


2.0541 


9.80 


2.2824 


1.85 


O.6151 


3.85 


i.348o 


5.85 


I.7664 


7.85 


2.0605 


9-85 


2.2875 


1.90 


0.641S 


3.90 


I .3610 


5.90 


1.7750 


7.90 


2.0668 


9.90 


2.2925 


1-95 


0.6678 


3-95 


1.3737 


5-95 


1.7834 


7.95 


2.0731 


9-95 


2.2976 


2.00 


0.6931 


4.00 


1.3863 


6.00 1. 79 1 8 


8.00 


2.0794 


10.00 


2.3026 


2.05 


0.7178 


4.05 


1.3987 


6.05 


I . 8000 


8.05 


2.0857 


10.25 


2.3273 


2.10 


0.7419 


4. 10 


1. 4010 


6. 10 


I.8083 


8.IO 


2.0918 


10.50 


2.3514 


2.15 


0.7654 


4.15 


1.4231 


6.15 


I. 8164 


8.15 


2.0988 


io.75 


2.3749 


2.20 


O.7885 


4.20 


1. 4351 


6.20 


I.8245 


8.20 


2. IO4I 


11 .00 


2.3979 


2.25 


0.8110 


4-25 


1 . 4469 


6.25 


I.8326 


8.25 


2. II02 


12.00 


2.4849 


2.30 


0.8329 


4.30 


1.4586 


6.30 


I . 8405 


8.30 


2. I 162 


13.00 


2.5626 


2-35 


0.8544 


4-35 


1. 4701 


6.35 


I.8484 


8.35 


2. 1222 


14.00 


2.639O 


2.40 


0.8755 


4.40 


I. 4816 


6.40 


I.8563 


8.40 


2.1282 


15.00 


2.7I03 


2-45 


0.8961 


4-45 


1.4929 


6.45 


I . 8640 


8.45 


2.1342 


16.00 


2.7751 


2.50 


O.9163 


4.5o 


1 . 5040 


6.50 


I. 8718 


8.50 


2 . I40O 


17.00 


2.8332 


2.55 


O.9361 


4.55 


I.5J5I 


6.55 


1.8795 


8.55 


2.1459 


18.00 


2.8903 


2.60 


o.9555 


4.60 


I.5260 


6.60 


I.8870 


8.60 


2.I5I8 


19.00 


2 . 9444 


2.65 


0.9746 


4.65 


1.5369 


6.65 


I.8946 


8.65 


2.1576 


20.00 


2.9957 


2.70 


0.9932 


4.70 


1.5475 


6.70 


I. 902 1 


8.70 


2.1633 


21 .00 


3.0445 


2-75 


1.0116 


4-75 


1. 558i 


6.75 


!.9095 


8.75 


2. 169O 


22.00 


3.0910 


2.80 


1 .0296 


4.80 


1.5686 


6.80 


1 .9169 


8.80 


2.1747 


23.00 


3.035 5 


2.85 


I.0473 


4.85 


1.5790 


6.85 


1.9242 


8.85 


2. 1804 


24.00 


3.1780 


2. go 


1.0647 


4.90 


1.5892 


6.90 


L93I5 


8.90 


2.l860 


25 .00 


3.2189 


2.95 


I. 0818 


4.95 


1.5994 


6.95 


T.9387 


8.95 


2.I9I6 


30.00 


3.3782 



200 ENGINEERING 

by the weight per cubic foot of steam at the pressure 
as measured will give the weight of steam consumed 
during one stroke. From this should be deducted the 
steam saved by compression as shown by the diagram, 
in order to get a true measure of the economy of the 
engine. Having thus determined the weight of steam 
consumed for one stroke, multiply it by twice the num- 
ber of strokes per minute and by 60, which will give 
the total weight consumed per hour. This divided by 
the horse power will give the rate per horse power per 
hour. 

Cylinder condensatiofi a?id re evaporation. When the 
exhaust valve opens to permit the exit of the steam 
there is a perceptible cooling of the walls of the 
cylinder, especially in condensing engines when a high 
vacuum is maintained. This results in more or less 
condensation of the live steam admitted by the open- 
ing of the steam valve; but if the exhaust valve is 
caused to close at the proper time so as to retain a 
portion of the steam to be compressed by the piston on 
the return stroke, a considerable portion of the water 
caused by condensation will be reevaporated into steam 
by the heat and consequent rise in pressure caused by 
compression. 

Ordinates. Parallel lines drawn at equal distances 
apart across the face of the diagram, and perpendic- 
ular to the atmospheric line. They serve as a guide to 
facilitate the measurement of the average forward 
pressure throughout the stroke, or the pressure at any 
point of the stroke if desired. 

Eccentric.. A mechanical device used in place of a 
crank for converting rotary into reciprocating motion. 
An eccentric is in fact a form of crank in which the 
crank pin, corresponding to the eccentric sheave, 



DEFINITIONS AND TABLES 201 

embraces the shaft, but owing to the great leverage at 
which the friction between the sheave and the strap 
acts, compared with its short turning leverage, it can 
only be used to advantage for the purpose named 
above. 

Eccentric throw is the distance from the center of the 
eccentric to the center of the shaft. This definition 
also applies to the term "radius of eccentricity." 

Eccentric position. The location of the highest point 
of the eccentric relative to the center of the crank pin, 
measured or expressed in degrees. 

Angular advance. The distance that the high point 
of the eccentric is set ahead of a line at right angles 
with the crank. In other words, the lap angle plus 
the lead angle. If a valve had neither lap nor lead, 
the position of the high point of the eccentric would 
be on a line at right angles with the crank; as for 
instance, the crank being at o° the eccentric would 
stand at 90 . 

Valve travel. The distance covered by the valve in 
its movement. It equals twice the throw of the eccen- 
tric. This refers to engines having a fixed cut off. In 
the case of an engine with a variable automatic cut off 
the travel of the cut off valve is regulated by the gov- 
ernor. 

Lap. The amount that the ends of the valve project 
over the edges of the ports when the valve is at mid 
travel. 

Outside or steam lap. The amount that the end of 
the valve overlaps or projects over the outside edge of 
the steam port. 

* Inside lap. The lap of the inside or exhaust edge of 
the valve over the inside edge of the port. 

Lead. The amount that the port is open when the 



202 ENGINEERING 

crank is on the dead center. The object of giving a 
valve lead is to supply a cushion of live steam which, 
in conjunction with that already confined in the clear- 
ance space by compression, shall serve to bring the 
moving parts of the engine to rest quietly at the end 
of the stroke, and also quicken the action of the piston 
in beginning the return stroke. 

Compression. Closing of the exhaust passage before 
the steam is entirely exhausted from the cylinder. 
A certain quantity of steam is thus compressed into 
the clearance space. 

Throttling governor. Used to regulate the speed of 
engines having a fixed cut off. The governor controls 
Ihe position of a valve in the steam pipe, opening or 
closing it according as the engine needs more or less 
steam in order to maintain a regular speed. 

Automatic or variable cut off. In engines of this type 
the full boiler pressure is constantly in the valve chest 
and the speed of the engine is regulated by the gov- 
ernor controlling the point of cut off, causing it to take 
place earlier or later according as the load on the 
engine is lighter or heavier. 

Fixed cut off. This term is applied to engines in 
which the point of cut off remains the same regardless 
of the load, the speed being regulated by a throttling 
governor as explained above. 

Isochronal or shaft governor. This device in which 
the centrifugal and centripetal forces are utilized, as 
in the fly ball governor, is generally applied to auto- 
matic cut off engines having reciprocating or slide 
valves. It is attached to the crank shaft and its func- 
tion is to change the position of the eccentric, which 
is free to move across the shaft within certain pre- 
scribed limits, but is at the same time attached to the 



ENGINEERING 



203 



Table 9. 
Areas and Circumferences of Circles. 



Diam. 


Area. 


Circum. 


Diam. 


Area. 


Circum. 


Diam. 


Area. 


Circum. 


•25 


.049 


.7854 


15.5 


18S.692 


48.694 


31 


754.769 


97.389 


• 5 


.1963 


1.5708 


16 


201.062 


50.265 


31-25 


766.992 


98.175 


1.0 


.7854 


3.1416 


16.25 


207.394 


5L05I 


3i-5 


799.3I3 


98.968 


1-25 


1. 2271 


3.9270 


16.5 


213.825 


51.836 


32 


804.249 


100.53 


1.5 


1. 7671 


4.7124 


17 


226.980 


53.407 


32.25 


816.86 


101.31 


2 


3.1416 


6.2832 


17-25 


233.705 


54.192 


33 


855.30 


103.67 


2.25 


3.9760 


7.0686 


17-5 


24O. 5 20 


54-978 


33.25 


868.30 


I04.45 


2.5 


4.9087 


7.8540 


18 


254-469 


56.548 


33-5 


881.41 


105.24 


3 


7.0686 


g.4248 


18.25 


261.587 


57.334 


34 


907.92 


106.81 


3-25 


8.2957 


I0.2IO 


18.5 


268.803 


58.119 


34.25 


921.32 


107.60 


3-5 


9. 62 1 1 


IO.995 


19 


283-529 


59.690 


34-5 


934.82 


108.38 


4 


12.566 


12.566 


19-25 


29I. O39 


60.475 


35 


962.11 


106.95 


4-25 


14.186 


13.351 


19-5 


298.648 


61.261 


35.25 


975.90 


110.74 


4.5 


15.904 


14.137 


20 


314.160 


62.832 


35-5 


989.80 


in. 52 


5 


I9-635 


I5.708 


20.25 


322.063 


63.617 


36 


1017.8 


113-09 


5-25 


21.647 


16.493 


20.5 


33O.064 


64.402 


36.25 


1032.06 


113.88 


5-5 


23.758 


17.278 


2f 


346.361 


65.973 


36.5 


1046.35 


114.66 


6 


28.274 


18.849 


21.25 


354-657 


66.759 


37 


1075.21 


116.23 


6.25 


30.679 


I9.635 


21.5 


363.05I 


67.544 


37-25 


1089.79 


117.01 


6.5 


33.183 


20.420 


22 


380.I33 


69.115 


37-5 


1104.46 


117. 81 


7 


38.484 


21.991 


22.25 


388.822 


69.900 


38 


H34-II 


119.38 


7-25 


41.282 


22.776 


22.5 


397.6o8 


70.686 


38.25 


1149.08 


120.16 


7-5 


44.178 


23.562 


23 


415.476 


72.256 


38.5 


1164. 15 


120.95 


8 


50.265 


25.132 


23.25 


424-557 


73.042 


39 


1194.59 


122.52 


8.25 


53-456 


25.918 


23-5 


433.731 


73-827 


39.25 


1209.95 


123.30 


8.5 


56.745 


26.703 


24 


452.390 


75.398 


39-5 


1225.42 


124.09 


9 


63.617 


28.274 


24.25 


461.864 


76.183 


40 


1256.64 


125.66 


9-25 


67.200 


29.059 


24.5 


47I.436 


76.969 


40.25 


1272. 3g 


126.44 


95 


70.882 


29.845 


25 


49O.875 


78.540 


40.5 


1288.25 


127.23 


10 


78.540 


3I.4I6 


25-25 


500.741 


79.325 


4i 


1320.25 


128.80 


10.25 


82.516 


32.201 


25.5 


5IO.706 


80.IIO 


41.25 


1336.40 


129.59 


10.5 


86.590 


32.986 


26 


530.930 


81.681 


41.5 


1352.65 


130.37 


11 


95-033 


34-557 


26.25 


54LI89 


82.467 


42 


1385.44 


I3I-94 


11.25 


99.402 


35-343 


26.5 


551-547 


83.252 


42.25 


1401.98 


132.73 


11. 5 


103.869 


36.128 


27 


572.556 


84.823 


42.5 


1418.62 


133.51 


12 


113.097 


37-699 


27.25 


583.208 


85.608 


43 


1452.20 


I35-08 


12.25 


II7-859 


38.484 


27.5 


593.958 


86.394 


43-25 


1469.13 


135.87 


12.5 


122.718 


39.270 


28 


615.753 


87.964 


43-5 


1486.17 


136.65 


13 


132.732 


40 840 


28.25 


626.798 


88.750 


44 


I52C53 


138.23 


13-25 


137.886 


41.626 


28.5 


637.941 


89.535 


44.25 


1537-86 


139.01 


13-5 


143.130 


42.411 


29 


660.521 


91.106 


44-5 


1555.28 


139.80 


14 


I53-938 


43-982 


29.25 


671.958 


91.891 


45 


1590.43 


I4I.37 


14-2 5 


I59-485 


44. 767 


29-5 


683.494 


92.677 


45-25 


1608.15 


142.15 


14.5 


165.130 


45-553 


30 


706.860 


94.248 


45-5 


1625.97 


142.94 


15 


176.715 


47-124 


30.25 


718.690 


'95.033 


46 


1661.90 


I44.5I 


15.25 


182.654 


47-Qog 


30.5 


730.618 


95.818 


46.25 


1680.01 


145.29 



£04 



DEFINITIONS AND TABLES 



Table 9 — Continued. 



Diam. 


Area. 


Circum. 


Diam. 


Area. 


Circum. 


Diam. 


Area. 


Circum. 


46.5 


1698.23 


146.08 


62 25 


3043-47 


195-56 


73 


4778.37 


245.04 


47 


1734.94 


147-65 


62.5 


3067.96 


196.35 


78. 25 


4809.05 


245.83 


47.25 


1753-45 


14S.44 


63 


3117.25 


197.92 


73.5 


4339.83 


246.61 


47-5 


[772.05 


149.22 


63.25 


3142.04 


198.71 


79 


4901.68 


248.19 


4 3 


1809.56 


150.79 


63.5 


3166.92 


I99-50 


79-25 


4932.75 


248.97 


48.25 


1828 46 


I5L58 


64 


3216.99 


201.06 


79 5 


4963.92 


249. 76 


48.5 


1S47.45 


152.36 


64.25 


3242.17 


201.85 


80 


5026.56 


25L33 


49 


1885.74 


153-93 


64-5 


3267.46 


202.68 


80.5 


5089.58 


252.90 


49-25 


1905.03 


154-72 


65 


33I8.3I 


204.20 


81 


5I53-00 


254-47 


49-5 


1924.42 


I55.50 


65.25 


3343-88 


204.99 


81.5 


5216.82 


256.04 


50 


1963.50 


157.08 


65-5 


3369-56 


205.77 


82 


5281.02 


257.61 


50.25 


1983.18 


157.86 


66 


3421..20 


207.34 


S2.5 


5345-62 


259.18 


50.5 


2002.96 


158.65 


66.25 


3447.16 


20S.13 


83 


5410.62 


260.75 


5i 


2042.82 


160.22 


66.5 


3473.23 


208.91 


33.5 


5476.00 


262.32 


51-25 


2062.90 


161.00 


67 


3525.66 


210.49 


84 


554L78 


263.89 


51.5 


2083.07 


161.79 


67-25 


3552.01 


211.27 


84.5 


5607.95 


265.46 


52 


2123.72 


163.36 


67-5 


3573.47 


212.06 


S5 


5674.51 


267.04 


52.25 


2144.19 


164.14 


68 


3631.68 


213.63 


85-5 


5741-47 


268.60 


52.5 


2164.75 


164.19 


68.25 


3658.44 


214.41 


86 


5808.81 


270.17 


53 


2206.18 


166.50 


68.5 


3685.29 


215.20 


86.5 


5876.55 


271.75 


53-25 


2227.05 


167.29 


69 


3739-28 


216.77 


37 


5944.66 


273.32 


53-5 


2248.01 


168.07 


69.25 


3766.43 


217-55 


87.5 


6013.21 


274.89 


54 


2290.22 


169.64 


69.5 


3793-^7 


218.34 


88 


6082.13 


276.46 


54-25 


2311.48 


170.43 


7o 


3848.46 


219.91 


88.5 


6151.44 


278.03 


54-5 


2332.83 


171. 21 


70.25 


3875-99 


220.70 


89 


6221.15 


279.60 


55 


2375-83 


172.78 


70.5 


390;. 63 


221. 48 


89.5 


6291.25 


281.17 


55-25 


2397.48 


173-57 


7i 


3959-2Q 


223.05 


90 


6371.64 


282.74 


55-5 


2419.22 


^74-35 


71-25 


3987-I3 


223.84 


90.5 


6432.62 


284.31 


56 


2463.01 


I75.92 


71-5 


4015.16 


224.62 


91 


6503.89 


285.88 


56.25 


2485.05 


176.71 


72 


4071.51 


226.19 


9i-5 


6573.56 


287.46 


56.5 


2507.19 


177-5 


72.25 


4099.83 


226.98 


92 


6647.62 


289.03 


57 


2551.76 


179.07 


72.5 


4128.25 


227.75 


92-5 


6720.07 


290.60 


57.25 


2574.19 


179.85 


73 


4135.39 


229.34 


93 


6792.92 


292.17 


57-5 


2596.72 


,180.64 


73-25 


4214. 11 


230.12 


93-5 


6866.16 


293-74 


58 


2642.08 


182.21 


73-5 


4242. 92 


230.91 


94 


6939-79 


295.31 


58.25 


2664.91 


182.99 


74 


4300.85 


232.48 


94-5 


7013.81 


296.88 


58.5 


2687.83 


183.78 


74-25 


4329-95 


233.26 


95 


7088.23 


298.45 


59 


2733-97 


185.35 


74-5 


4359.16 


234-05 


95-5 


7163.04 


300.02 


59-25 


2757.19 


186.14 


75 


4417.37 


235.62 


96 


7238.25 


301.59 


59-5 


2780.51 


1S6.92 


75-25 


4447-37 


236.40 


96.5 


73i3-8o 


303.16 


60 


2827.44 


188.49 


75-5 


4476.97 


237.19 


97 


7389-3I 


304.73 


60.25 


2851.05 


189.28 


76 


4536.37 


238.76 


97-5 


7466.22 


306.30 


50.5 


2874.76 


190.06 


,76.25 


4566.36 


2 39-55 


98 


7542.89 


307.88 


61 


2922 47 


191.64 


76.5 


4596.35 


240.33 


93-5 


7620.09 


309 44 


61.25 


2946.47 


192.42 


77 


4656.63 


241.90 


99 


7697.70 


311.02 


61.5 


2970.57 


193.21 


77 25 


4686.92 


242.69 


99-5 


7775.63 


312.58 


62 


3019.07 


194.78 


77-5 


47i7.3o 


243-47 


100 


7854.00 


314.16 



DEFINITIONS AND TABLES £05 

governor. The angular advance of the eccentric is 
thus increased or diminished, in fact is entirely under 
the control of the governor, and cut off occurs earlier 
or later according to the demands of the load on the 
engine. 

Adjustable cut off. One in which the point of cut off 
may be regulated or adjusted by hand by means of a 
hand wheel and screw attached to the valve stem, the 
supply of steam being regulated by a throttling gov- 
ernor. 

Questions 

i. What is absolute pressure? 

2. What is gauge pressure? 

3. W 7 hat is initial pressure? 

4. What is terminal pressure and how may it be 
ascertained theoretically? 

5. What is back pressure? 

6. Whatis absolute back pressure? 

7. What is meant by ratio of expansion? 

8. What does the term wire drawing mean when 
applied to an indicator diagram? 

9. What is condensor pressure? 

10. What does the term vacuum imply? 

11. What is absolute zero? 

12. What is meant by the term piston displacement? 

13. What is piston clearance? 

14. What is steam clearance? 

15. What is a horse power? 

.16. What is meant by piston speed? 

17. Define Boyle's law of expanding gases. 

18. What is an adiabatic curve? 

19. What is an isothermal curve? 

20. What is the first law of thermodynamics? 

21. What is the unit of work? 



-206 



ENGINEERING 



22. Define the first law of motion. 

23. What is momentum? 

24. What is the maximum theoretical duty of steam? 

25. What is meant by the term steam efficiency? 

26. How may the term engine efficiency be defined? 

27. What is meant by the term efficiency of the 
plant, and how may it be ascertained? 

28. How is the horse power constant of an engine 
found, and what does it mean? 

29. What are common logarithms? 

30. What are hyperbolic logarithms, and how are 
they found? 

31. What are ordinates as applied to an indicator 
diagram? 

is an eccentric? 

is meant by the throw of an eccentric? 
is meant by position of the eccentric? 
is angular advance? 
is valve travel? 
s lap? 

s inside lap? 
s outside lap? 
s lead? 

s a throttling governor? 
s meant by the term fixed cut off? 
s meant by an automatic cut off? 
s an isochronal governor? 
s an adjustable cut off? 



32. 


What 


33- 


What 


34- 


What 


35- 


What 


36. 


What 


37- 


What 


38. 


What 


39- 


What 


40. 


What 


41. 


What 


42. 


What 


43- 


What 


44. 


What 


45- 


What 



CHAPTER IX 

DIAGRAM ANALYSIS 

Diagram analysis — Figure illustrating the various points in an 
indicator diagram — Disadvantage of unequal cut off — Dia- 
gram from compound condensing engine — Rules for finding 
M. E. P. when the initial and terminal pressures are known, 
and the ratio of expansion — Equalizing the work done in the 
high and low pressure cylinders — Misleading diagrams caused 
by dirt in indicator cylinder — Diagrams showing effect of 
cramped exhaust — Table of factors for calculating the steam 
consumption fiom the terminal pressure. 

In the following study of indicator diagrams all the 
illustrations are reproductions of actual diagrams taken 
under ordinary working conditions. Figs. 50 and 51 
are here introduced in order to define the different 




FIGURE 50. 

points, lines and curves. Fig. 50 was taken from a 
large vertical engine with the corliss valve motion. 

The engine being of slow speed and extremely long 
stroke (10 ft.) with a clearance of but 1 per cent., the 
compression beginning at C and ending at B is some- 
what lighter than is ordinarily given to shorter stroke 
207 



208 



ENGINEERING 



engines. From B to D is the admission line, which 
being practically perpendicular to the atmospheric 
line A, shows sufficient lead and ample port area. 
From D to E is the steam line. Cut off occurs at E, 
and from E to F is the expansion curve. At F the 
point of release is quite sharply defined, as it should 
be. From F to G is the exhaust line,, and from G to C 
the line of back pressure, sometimes called the line of 
counter pressure for the reason that the pressure indi- 
cated by it acts counter or in opposition to the forward 
pressure of the steam on the piston. This engine, is a 




FIGURE 51. 



simple condensing engine and the nearness of the 
back pressure line to the line of perfect vacuum V 
shows that an excellent vacuum was maintained in the 
condenser. 

Fig. 51 is from a Buckeye automatic cut off engine 
having a shaft governor and what is termed a riding 
cut off, that is the cut off valve slides to and fro on 
the back of the main valve. The engine is horizontal 
non-condensing, the cylinder being 28 in. bore by 56 
in. stroke, and, at the time the diagram was taken, 



DIAGRAM ANALYSIS 209 

developed 357. 58 horse power with a piston speed of 
728 ft. per minute. The steam consumption per I. H. 
P. per hour was 26 lbs., a rather high rate, but this was 
owing to the fact that the engine was located too far 
from the boilers, and as there were a large number of 
elbows in the steam pipe the pressure was greatly- 
reduced at the engine. Thus wire drawing of the 
steam was caused, which is plainly indicated by the 
downward inclination of the steam line, D E. 

In a well proportioned engine having a steam pipe 
of sufficiently large area, the steam line should paral- 
lel the atmospheric line up to the point of cut off. 
Fig. 51 indicates proper release of the steam at F, and 
the back pressure from G to C, which is 3 lbs. above 
the atmospheric line, shows a reasonably free passage 
of the exhaust steam. 

Figs. 52 to 57 illustrate diagrams from three new 
vertical corliss engines supplying power for an electric 
lighting plant, which the author was requested to test 
and adjust after they had been in operation a few 
months. The valves had previously been set by the 
erecting engineer at the time the engines were set up. 
Each one of these engines exhausted into a separate 
condenser of the Jet type, into which the condensing 
water was forced under pressure and from which the 
overflow was discharged by gravity into a sewer. 
There was no air pump and as a consequence the 
vacuum maintained was very low, usually from 10 to 
15 in., and at times still less, so that the beneficial 
results of condensing were only partially realized. 

For convenience the diagrams from each engine will 
be treated in numerical order, beginning with engine 
No. I. This engine was 24 x 48 in., running 70 R. P. 
M., with a boiler pressure of 68 lbs. A 40 spring was 



210 



ENGINEERING 



used in the indicator. The principal defect was the 
lack of sufficient lead on both ends, as indicated by 
the inclination inward of the admission lines and the 
rounded corners of the steam lines at the beginning of 




FIGURE 52. 

the stroke. (See Fig. 52.) There was also more com- 
pression, especially on the bottom end, than was neces- 
sary, considering the size of the engine and the speed. 
The necessary changes having been made, the indi- 
cator was again applied and the diagram Fig. 53 was 




FIGURE 53. 



obtained, which shows the distribution of the steam to 
be satisfactory, although at the time of taking this 
diagram the boiler pressure was only 60 lbs., while it 
should have been 68 or 70 lbs., because with the latter 



DIAGRAM ANALYSIS 



211 



pressure still better results could have been attained. 
The I. H. P. was 235 and the steam used per I. H. P. 
per hour was 18 lbs. 

Fig. 54 is the original diagram from engine No. 2, 




figure 54. 

and shows bad valve adjustment all around, with the 
exception of lead on the top end. The variation in 
the points of cut off is the worst feature; cut off 
taking place on the bottom at 29 per cent, of the 
stroke, while on the top end it does not occur until 



__1 



-A 

-V 



FIGURE 55. 



the piston has traveled through 42 per cent, of the 
stroke. There is more compression also than is 
needed. This engine was 18 x 42 in., running at a 
speed of 78 R. P. M., and the steam consumption, 



2F2 



ENGINEERING 



according to diagram Fig. 54, was 33 lbs. per I. H. P. 
per hour. Having equalized the cut off and reduced 
the compression by making the necessary changes in 
the valve gear, the indicator was again applied, result- 
ing in diagram Fig. 55, which maybe considered prac- 




FIGURE 56. 



tically perfect. The boiler pressure was 68 lbs. and 
the spring used was a No. 40. The steam consump- 
tion was reduced to 22 lbs. per I. H. P. per hour as 
compared to 33. lbs. in Fig. 54. 

Figs. 56 and 57 represent diagrams from engine No. 
3, which w£s the same size as No. 1, viz., 24x48 in., 




FIGURE 57. 



and running at 72 R. P. M. The original diagram, 
Fig. 56, shows too little lead on both ends, but espe- 
cially on the top. There is also lack of compression 
on the bottom end. The boiler pressure was 60 lbs. 
and the scale of spring 40. Fig. 57, taken after the 



DIAGRAM ANALYSIS 



21.3 



necessary adjustments had been made, shows much 
better valve performance. The horse power developed 
was 251 and the steam consumption was 20.5 lbs. per 
I. H. P. per hour. The rather high rate of steam 
consumption for this engine as compared with engine 
No. 1, which was the same size but consumed only 18 
lbs. of steam per I. H. P. per hour, was due to two 
causes. First, a low vacuum; second, low initial pres- 
sure necessitating a late cut off. 

Figs. 58 to 61 , inclusive, are diagrams from a Bullock 
horizontal non-condensing corliss engine which had 




figure 58. 



been running about eight or nine months when it fell 
to the author's lot to apply the indicator to the engine, 
not only for the purpose of adjusting the valve motion, 
but also to make a series of tests for the purpose of 
ascertaining the amount of power delivered by the 
engine to each one of several different departments 
which were receiving power from this source. 

The dimensions of the engine were as follows: bore 
of cylinder, 32 in.; stroke, 5 ft. At the time Fig. 58 
was taken the engine was making 62 R. P. M. and the 
boiler pressure was only 50 lbs. A 30 spring was 
used. Although the load on the engine was very light 



214 



ENGINEERING 



at the time, yet the diagram served as a guide to some 
extent in setting the valves, and by taking off the bon- 
nets from the valve chests and making the necessary 
changes in the adjustment by the marks on the valves 




FIGURE 59. 

a pretty fair job was made of it, as will be seen by 
referring to Fig. 59. The reducing motion was a 
pantograph, described in Chapter VIII, and as it is 
very easy to vary the travel of the paper drum with 
this motion, diagrams of different lengths were taken 
until the one which appeared to be the most satisfac- 




FIGURE 60. 



tory was obtained. The slight hump in the expansion 
curve immediately after cut off was probably caused 
by a speck of dirt or grit which momentarily checked 
the indicator piston on the down stroke. The com- 



DIAGRAM ANALYSIS 



215 



pression on the crank end is not sufficient and the 
exhaust valve rod on that end was slightly lengthened, 
resulting in the production of diagram Fig. 60. In 
this diagram the familiar hump in the crank end expan- 
sion curve reappears, but in a different location, being 
nearer the end of the stroke. It will also be noticed 
that the length of Fig. 60 has been considerably 
reduced from that of Figs. 58 and 59, it being about 
one inch shorter. 



Hc*d 




FIGURE 61. 



The boiler pressure and the load on this engine were 
gradually increased from time to time, from 50 lbs. 
and a light load, (as shown by Fig. 58) to 60 lbs. and 
335 horse power, (as indicated by Fig. 59 taken some 
three months later) and when Fig. 61 was taken, about 
two years and eight months later, the boiler pressure 
had been increased to 87 lbs. and the I. H. P. was 
over 700. 

Diagram Fig. 61 shows good economy in the use of 



nc> 



ENGINEERING 



steam in spite of the fact that the cut off occurs rather 
late. There is no back pressure worth mentioning, the 
back pressure line forming part of the atmospheric 
line through the largest part of the stroke. The reason 
for this is that the areas of the exhaust ports as well 
as the exhaust pipe were sufficiently large to permit a 
free passage for the steam. The exhaust pipe, also, 
was made as short and direct as possible and all super- 
fluous elbows were dispensed with. The steam con- 

I5h 




figure 62. 



sumed per I. H. P. per hour as per diagram Fig. 61 
was 22.3 lbs., and the horse power developed was 710.6. 
Figs. 62 to 64, inclusive, represent diagrams from a 
Buckeye engine 24 x 48 in., and are introduced for the 
purpose of emphasizing the need of caution and good 
judgment in setting valves by the indicator when the 
load on the engine is variable. Fig. 62, which was the 
first to be taken, would seem to indicate that the valve 
was badly adjusted, but when Fig. 63 was taken imme- 
diately afterwards, the cause of the trouble became 
apparent. The engine was furnishing power for 



DIAGRAM ANALYSIS 



217 



operating an electric street railway on a small scale, 
and the variation in the points of cut off was caused 
by the stopping and starting of the cars. 

Fig. 63 is a notable example of the quick and deli- 
cate action of the shaft governor, as it will be seen 
that during four successive revolutions there was a 
different load each time, as shown by the diagram 
from the crank end. 

























^ 


^ 


\ 




















cy 


^ 
^ 


\ 




















^s 


N. 






















a. 


*fc 






















Ui 


<*> 






















sr 


* 


5 




<5^ 






v. 


*»». 


^ ^ W 






m 


M 


s\ 







•^ 
-S 


^ 











FIGURE 63- 



Fig. 64 was secured by quick manipulation of the 
instrument when it was known that the load was to be 
steady for a few seconds. 

Fig. 65 is from an Atlas single valve automatic cut 
off engine with shaft governor. This engine was 
16 x 24 in., running at 105 R. P. M., and at the time 
the diagram was taken the boiler pressure was only 50 
lbs. The spring used was a No. 30. The diagram is a 



218 



ENGINEERING 



fairly good one for the type of engine. Owing to the 
variation in the angular advance of the single eccentric 




actuated by a shaft governor, the degree of compres- 
sion varies with the point of cut off in the single valve 
engine, the compression being higher with an early 




figure 65. 



cut off than it is when cut off occurs later in the 
stroke. The loop at A is caused by too much lead 



DIAGRAM ANALYSIS 



219 



which, together with the compression, caused a 
momentary rise in the pressure above the normal. 
The lead at B is approximately correct. The differ- 



HP 



ence in terminal pressures at C and D is the result of 
shifting of the points of cut off caused by variations in 
the load. The back pressure lines are almost identical 
with the atmospheric line, showing that the exhaust is 




figure 67. 



in no way restricted or cramped. I. H. P. is 65.7 and 
steam consumption 21 lbs. per I. H. P. per hour. 

Figs. 66 and 67 are diagrams taken from a cross 



220 ENGINEERING 

compound condensing corliss engine. The high 
pressure cylinder was 24 x 48 in., and the low pressure 
cylinder was 44 x 48 in. The steam from the high 
pressure exhausted into a receiver and from thence 
into the low pressure cylinder. The receiver pressure 
was 5.3 lbs. above atmospheric pressure. The ratio of 
piston areas was 3.36 toi. That is, the area of the low 
pressure piston was 3.36 times the area of the high 
pressure piston, which was about the correct ratio for 
the pressure carried, viz., 84 lbs. gauge or 99 lbs. 
absolute. A No. 40 spring was used on the high 
pressure and a No. 12 on the low pressure cylinder. 
The number of expansions in the two cylinders was 14. 
Thus, the ratio of expansion in the high pressure cylin- 
der was 4.5 and in the low pressure the ratio was 3.1. 
Then 4.5 x 3.1 = 14; or, Thus, initial pressure = 99 lbs. 
absolute, terminal pressure in L. P. cylinder = 7 lbs. 
absolute; then 99 -*- 7 = 14. 

To illustrate the process of finding the M. E. P. with- 
out the use of ordinates when the absolute initial and 
terminal pressures and the number of expansions in 
each cylinder are known, the following problems will 
be worked out: 

Find M. E. P. in L. P. cylinder. 

First, find initial pressure. 

Rule. T. P. multiplied by number of expansions. 
Thus, 7x3.1 = 21.7 lbs. absolute initial pressure in 
L. P. cylinder. 

Second, find mean forward pressure (M. F. P.). 

Rule. Multiply initial pressure by hyperboli< 
logarithm of number of expansions plus I, and divid< 
product by number of expansions. Thus the hyper 
bolic logarithm of 3. 1 = 1. 13 14, to which add 1 = 2.1314 
Then 2L7 ^- 1314 = 14.9 lbs. M. F. P. Deduct from 



DIAGRAM ANALYSIS 221 

this the back pressure, which was 5 lbs. absolute. 
Thus, 14.9- 5 = 9.9 lbs. M. E. P. in L. P. cylinder. 

Next find M. E. P. in H. P. cylinder. 

First, find T. P. in H. P. cylinder. 

This will equal the initial pressure in the L. P. 
cylinder + 2 per cent for loss in the receiver. Thus, 
21.7 + .4 = 22.1 lbs., terminal pressure in H. P. cylinder- 
Second, find initial pressure in H. P. cylinder. 

Ride. Multiply T. P. by number of expansions. 
Thus, 22.1 x 4.5 =99.4 lbs., absolute initial pressure in 
H. P. cylinder. 

Third, find mean forward pressure (M. F. P.). 

The hyperbolic logarithm of 4.5 = 1. 5041, add 
1=2.5041. Then 55^41^1 =55 lbs., M. F. P. in H. 
P. cylinder. Deduct back pressure 22.1; thus, 55 lbs. 
-22.1 lbs. = 32.9 lbs., M. E. P. in H. P. cylinder. 

The ratio of piston areas being 3.36 to I, it may be 
of interest to pursue the subject a little farther and 
ascertain how the distribution of the steam in the two 
cylinders corresponds to the ratio of areas. The ratio 
and pressures may be expressed as follows: 
Ratio of areas — H. P. cylinder, 1; L. P. cylinder, 3.36. 
M. E. P. — H. P. cylinder, 32.9; L. P. cylinder, 9.9 lbs. 
which is very nearly correct; sufficiently so for all 
practical purposes, and clearly demonstrates that with 
the intelligent use of the indicator it is possible to so 
adjust the valves and establish the points of cut off on 
a compound or triple expansion engine that the work 
done in each cylinder will be practically the same. 
As for instance, the product of the area of the H. P. 
piston and the M. E. P. = 14,883.6 lbs., and that of the 
L. P. piston x M. E. P. = 15,052.9 lbs., a difference 
of only 169.3 lbs. If the two products had been equal, 



222 



ENGINEERING 



the horse power exerted in the two cylinders would 
have been the same. As it was, the horse power of 
the H. P. cylinder was 263.4 and that of the L. P. 
cylinder was 266.4, showing a difference of only three 
horse power in the amount of work done in each 
cylinder. 

Fig. 68 was taken from one of a pair of Fishkill Cor- 
liss engines connected to a common crank shaft. The 
engines were each 24 x 48 in., and run at 65 R. P. M., 
with a boiler pressure of 65 lbs. They were equipped 
with a jet condenser and a bucket plunger air pump 
served for both engines. These engines had been in 




figure 68. 



continuous service for nearly seventeen years when the 
author was called upon to indicate them and adjust 
the valves. A diagram taken at the same time from 
the mate of this engine was very nearly an exact 
counter part of Fig. 68. The horse power, as shown 
by Fig. 68, was 248, and the steam per I. H. P. per 
hour was 15.2 lbs. The vacuum gauge showed 27 in. 
and a 50 spring was used. 

Figs. 69 and 70 are from an old Fishkill corliss 
engine 16 x 42 in., to which the author applied the 
indicator after he had set the valves, according to the 
ordinary rules for valve setting, by the marks placed 



DIAGRAM ANALYSIS 



223 



on the ends of the valves and valve chests. These 
diagrams are introduced especially for the purpose of 
showing the need of exercising the greatest of care to 
prevent dirt or grit of any kind from getting into the 




FIGURE 69. 

indicator cylinder. After the indicator pipes had been 
blown out sufficiently, as it was thought, the indicator, 
which was a thoroughly reliable instrument, was 
attached and diagram Fig. 69 was obtained. It 
showed the valve adjustment to be very nearly correct, 
but the perfectly straight steam lines and the sharp 




FIGURE 70. 



corners and sudden drop at cut off were a puzzle, espe- 
cially in an old engine where the valves and valve 
seats were known to be much worn down. After 
taking several more diagrams with precisely the same 



224 ENGINEERING 

result, the indicator was removed, and upon taking 
out the piston a quantity of dirt was found on it and 
also on the inside of the cylinder. This fully 
explained the cause of the sharp corners, etc., on the 
diagram. After the indicator had been cleaned and 
oiled it was again connected and Fig. 70 was produced, 
which is a truthful presentation of the performance of 
the steam in the cylinder. 

Many diagrams are misleading, owing to causes 
similar to the above, and a diagram with too sharp 
angles at cut off or release should be regarded with 
suspicion until it is proved beyond all doubt to be 
truthful. 




FIGURE 71. 

Fig. 71 represents a diagram from a vertical non- 
condensing engine 14 x 16 in. with riding cut off, 
which the author was called upon to adjust. This 
engine was nearly new, having been run but a few 
months, and although the size of it was ample to do 
all the work required, yet it had failed, so far, to supply 
one-half the power needed. After taking the diagram 
and making a few outside investigations, the cause of 
the trouble was apparent. Indeed, the wonder was that 
the engine had supplied as much power as it had 
under the circumstances. 

First. It was situated too far from the boiler plant, 
being fully 1,200 ft., -and although a pressure of 85 lbs. 



DIAGRAM ANALYSTS 225 

was carried at the boilers and the steam was conveyed 
through a 6-inch pipe, yet owing to the many drains on 
the pipe for heating buildings, running other small 
engines, etc., by the time the steam reached the engine 
in question the pressure was reduced so much that a 30 
spring was found to be too strong, although that was 
the scale of Fig. 71. 

Second, the end of the exhaust pipe was found to 
be submerged in a nearby pond of water to which it 
had been carried, probably with a view of making a 
condensing engine out of it! It was also found that 




FIGURE 72. 

there were no less than four superfluous elbows in the 
exhaust pipe that could easily be dispensed with. The 
diagram shows that the cut off was practically useless. 
That the back pressure was nearly 6 lbs. above the 
atmosphere, and that the engine was using 55 lbs. of 
steam and 7 lbs. of coal per horse power per hour, all 
of which conditions were about as bad as they could 
be. 

After increasing the lead and adjusting the cut off a 
No. 16 spring was used and Fig. 72 was produced 
which, although still showing late admission, is an 
improvement over the original diagram. The initial 



226 ENGINEERING 

pressure being only 30 lbs, above the atmosphere, 
further work with the indicator was deferred until 
changes were made in the steam and exhaust pipes, 
by which the initial pressure was increased to 55 lbs. 
and the exhaust pipe was freed of extra turns and 
raised from its watery, grave into the open air. The 
engine has since then given perfect satisfaction. 

Fig. 73 is from a Buckeye automatic cut off engine 
18 x 36 in. The engine had been running for several 
years with the valves in the condition shown by the 
diagram, and in the meanwhile, the load having been 
increased from time to time, the engine finally refused 




FIGURE 73. 

to run up to speed and something had to be done. 
The superintendent of the plant said that he had an 
idea that something was the matter with the engine 
but could not ascertain what it was, and so he finally 
called upon the author to apply the indicator. The 
result was that diagram Fig. 73 was obtained, showing 
that the principal cause of the trouble was unequal cut 
off. After equalizing the cut off and increasing the 
lead on the crank end by a small fraction diagram 
Fig. 74 was taken, and after this the engine gave no 
further trouble. The depression in the steam lines 
might have been rectified to some extent by increasing 






DIAGRAM ANALYSIS 227 

the boiler pressure, thus giving a higher initial pressure 
and an earlier cut off. The speed of the engine was 
94 R. P. M., with a boiler pressure of 70 lbs. A 40 
spring was used with the indicator. 

In order to more fully illustrate the process of ascer- 
taining the M. E. P. without dividing the diagram into 
ordinates, the following computation is given together 
with rules, etc. In this process two important factors 
are necessary, viz., the absolute initial pressure and 
the absolute terminal pressure, and they can both be 
obtained from the diagram by measuring with the 




figure 74. 

scale adapted to the spring used. Thus, in Fig. 74 the 
absolute initial pressure measured from the line of 
perfect vacuum V to line B is 'jy lbs., and the absolute 
terminal pressure measured from V to line B' is 21 lbs. 
The ratio, or number of expansions, is found thus: 

Rule. Divide the absolute initial pressure by the 
absolute terminal pressure; thus, yj -5- 21 = 3.65 = num- 
ber of expansions. 

Second. Find mean forward pressure. 

Rule. Multiply absolute initial pressure by the 
hyperbolic logarithm of number of expansions plus I, 
and divide product by number of expansions. Thus, 



228 



ENGINEERING 



referring to Table 8, it will be seen that the hyperbolic 
logarithm of 3.65 is 1.2947, to which 1 must be 



added. Then 



48.4 lbs., which is the abso- 



lute mean forward pressure. From this deduct 
the absolute back pressure, which is 16 lbs. or 1 lb. 
above atmosphere; thus, 48.4- 16= 32.4 lbs. M. E. P. 

Third. Find I. H. P. 

Area of piston minus one-half area of rod x M. E. P. 
x piston speed in feet per minute, divided by 33,000. 

Ti_ /i.u J' i. c J U • „ • \ 250.96X32.4X564 

lnus (the diameter or rod being 3 in.), ^^ = 

138.9 I. H. P. 

The steam consumption per I. H. P. per hour may 
also be computed by means of Table 10, which was 
originally calculated by Mr. Thomson, and is based 
upon the following theory: 

TABLE 10. 



T. P. 


w. 


T. P. 


w. 


T. P. 


w. 


3 


117.30 


13 


466.57 


23 


798.10 " 


3-5 


135.75 


13-5 


483.43 


23-5 


814.39 


4 


153-88 


14 


500.22 


24 


830.64 


4-5 


171.94 


14.5 


517.07 


24.5 


846.96 


5 


186.75 


15 


533.85 


25 


863.25 


5-5 


207.60 


15-5 


550.64 


25.5 


879.49 


6 


225.24 


16 


567-36 


26 


895.70 


6.5 


242.97 


16.5 


584.10 


26.5 


911.86 


7 


260.54 


17 


600. 78 


27 


927.99 


7-5 


278.06 


17-5 


617.40 


27-5 


944- 07 


8 


295-44 


18 


633.96 


28 


960.12 


8.5 


312.80 


18.5 


650.46 


28.5 


976.27 


9 


330.03 


19 


666.90 


29 


992.38 


9-5 


347.27 


19-5 


683.38 


29-5 


1008.46 


10 


364.40 


20 


699.80 


30 


1024.50 


10.5 


381.57 


20.5 


716.27 


30.5 


1040.51 


11 


398.64 


21 


732.69 


31 


1056.48 


11. 5 


415-73 


21-5 


749-06 


31-5 


1072.42 


12 


432.72 


22 


765.38 


32 


1088.32 


12.5 


449.69 


22.5 


781.76 


32.5 


1104.35 



DIAGRAM ANALYSIS 229 

A horse power = 33,000 ft. lbs. per minute, or 1,980,- 
000 ft. lbs. per hour, or 1,980,000 x 12 = 23,760,000 in. 
lbs. per hour, meaning that the same amount of energy 
required to lift 33,000 lbs. one foot high in one minute 
of time would lift 23,760,000 lbs. one inch high in one 
minute of time. Now if an engine were driven by a 
fluid that weighed one pound per cubic inch, and the 
mean effective pressure of this fluid upon the piston 
was one pound per square inch, it would require 
23,760,000 lbs. of the fluid per horse power per hour. 
But, if in place of the heavier fluid we substitute pure 
distilled water of which it requires 27.648 cu. in. to 
weigh one pound, the consumption per I. H. P. per 
hour will be considerably less; as, for instance, 23,760,- 
000-27.648 = 859,375 lbs., which would be the rate 
per hour of the water driven engine if the M. E. P. of 
the water was one pound per square inch and if the 
M. E. P. was increased to 20 lbs.; then twenty times 
more power would be developed with the same volume 
of water, but the weight of water consumed per H. P. 
per hour would be proportionately less. Now if the 
engine is driven by steam it will consume just as 
much less water in proportion as the water required to 
make the steam is less in volume than the steam used. 
Therefore if the above constant number, 859,375, be 
divided by the M. E. P. of any diagram and by the 
volume of the terminal pressure, the quotient will be 
the water (or steam) consumption per I. H. P. per 
hour. 

Referring to Table 10, the numbers in the W columns 
are the quotients obtained by dividing the constant, 
859,375, by the volumes of the absolute pressures 
given in the columns under T. P. and which represent 
terminal pressures. The table is considerably abridged 



230 ENGINEERING 

from the original, which was very full and complete, 
the pressures advancing by tenths of a pound from 3 
bs. to 60 lbs.; but it is seldom that in ordinary practice 
there is needed such accuracy. If at any time, how- 
ever, a diagram should show a terminal pressure not 
given in the table, the correct factor for that pressure 
can be easily found by dividing the constant 859,375, 
by the relative volume of the pressure as found in 
Table 5 of the properties of saturated steam given in 
another chapter. 

Referring again to Fig. 74, it is seen that the^ ter- 
minal pressure is 21 lbs. absolute, and by reference to 
Table 10 and glancing down column T. P. until 21 is 
reached, it will be seen that the number opposite in 
column W is 732.69. This number divided by the M. 
E. P. of the diagram Fig. 74, which is 32.4 lbs., gives 
22.6 lbs. per I. H. P. per hour as the steam consump- 
tion. The rate thus found makes no allowance for 
clearance and compression, however, and these two 
very important items will be treated in a succeeding 
chapter together with the method of correction for the 
above, viz., clearance and compression, as they enter 
largely into the steam economy of an engine. 

Questions 

1. What effect has back pressure upon the work of 
an engine? 

2. Name some of the causes of wire drawing of the 
steam. 

3. What relation should the steam line of an indi- 
cator diagram bear to the atmospheric line? 

4. What is the effect of insufficient lead upon the . 
admission line of a diagram? 



DIAGRAM ANALYSIS 231 

5. How does an unequal cut off affect the working 
of an engine? 

6. How is the number of expansions in a compound 
engine ascertained? 

7. What is the rule for finding the initial pressure by 
calculation? 

8. Give the rule for finding the mean forward 
pressure. 

9. When the M. F. P. is known, how may the mean 
effective pressure be found? 

10. How should the steam be distributed in the 
cylinders of a compound engine? 

11. What is the rule for finding the horse power 
developed by an engine? 

12. What is meant by the steam consumption of an 
engine? 

13. What is considered an economical rate of steam 
consumption for a non-condensing engine? 

14. What is a fairly good rate of steam consumption 
for a condensing engine? 



CHAPTER X 
DIAGRAM ANALYSIS— CONTINUED 

Diagram analysis continued — Corliss Centennial engine and dia- 
grams from it— Calculating steam consumption from indicator 
diagrams — Clearance and compression, and how to correct a 
diagram for the same — How to estimate the theoretical clear- 
ance from a diagram — Measuring the volume of the clearance 
space with water — The theoretical expansion curve — Illustra- 
tion of hyperbolic law in its application to the expansion of 
gases — The adiabatic curve and how to draw it — Power cal- 
culations — Method of finding the M. E. P. of a diagram — The 
planimeter and how to use it. 

Figs. 75 to 77 are reproductions of diagrams taken 
by the author from the once famous engine built by 
Geo. H. Corliss for the Centennial Exposition which 
was held at Philadelphia in 1876. A brief description 
of this engine may not be out of place here, as it will 
enable the reader to study the diagrams to a better 
advantage. 

This engine is, in fact, two simple condensing beam 
engines, exactly alike in every detail, standing verti- 
cal side by side and connected to a common- crank 
shaft by means of the working beams overhead which 
are pivoted at their centers to the A frame of the 
engine. The cylinders are 40 in. bore by 10 ft. stroke 
and the engine runs at a speed of 36 R. P. M., thus 
giving a piston speed of 720 ft. per minute. The valve 
gear is of the regular corliss type adapted to a vertical 
engine, and motion is transmitted from the eccentric 
through the medium of a rock shaft placed horizontally 
on the frame. The steam and exhaust valves are 
232 



DIAGRAM ANALYSIS 



233 



located in the cylinder heads, thereby reducing the 
clearance to 1.5 per cent. Each engine has its own 
jet condenser and air pump, which latter is of the 
regular bucket plunger type and receives its motion 
from the overhead beam through long connecting rods. 
The crank shaft is 18 in. in diameter and carries a gear 
fly-wheel 30 ft. in diameter, weighing 56 tons, the 
teeth of which mesh into another gear wheel 10 ft. in 
diameter carried on the jack shaft through which the 
power is transmitted to the various departments of the 
works. The face of the rim of the gear wheel is 24 in. 




figure 75 



in width, which allows the length of the teeth to be 
24 in., while the pitch, or distance from center to cen- 
ter of the teeth, is 5 in. The steam pipe is 18 in. inside 
diameter and the cylinders are jacketed with live 
steam. 

This engine showed remarkable economy in the use 
of steam when working at or near the capacity for 
which it was designed by Mr. Corliss, which was 1,400 
horse power. At the time Fig. 75 was taken the load 
was 1,122 horse power and the boiler pressure was 32,5 
lbs. gauge, or 47.5 lbs. absolute. The spring used was_ 



234 ENGINEERING 

a No. 20, although a much better appearing diagram 
would have been obtained by using a No. 30 spring. 

The diagram shows very slight compression, but the 
lead is correct. The point of cut off is not so clearly 
defined as it should be, and the author attributes the 
cause of this to the spring being too weak for the 
reason that when Fig. 76 was taken some eight months 
later from the same end of the same cylinder, but with 
a spring of the proper tension for the pressure, the 
point of cut off is much more plainly defined. (See 
Fig. 76.) 




FIGURE 76. 

The absolute initial pressure, as shown by Fig. 75, 
was 47.5 lbs., and the absolute terminal pressure was 
8.5 lbs. The ratio of expansion would therefore be 
47-5 "*" 8-5 = 5-6. The steam consumption per I. H. P. 
per hour was 14 lbs. 

Fig. JJ is from the same engine, and is here intro- 
duced for the purpose of showing the great advantage 
resulting from a good vacuum. In fact the largest 
portion of the work in this case was done through the 
help of the vacuum, as indicated by much the largest 
portion of the area of the diagram being below the 
line of atmospheric pressure. The diagram would 
appear to be a kind of connecting link between the 



DTAGRAM ANALYSIS 



23.5 



times of Watt and Newcomen, when the vacuum did 
all the work, and these modern times of high steam 
pressure. 

The circumstances under which Fig. 77 was obtained 
were as follows: At certain times it became necessary 
to run a part of the shops overtime, and the load at 
such times being light, the boiler pressure was allowed 
to drop to the point at which the engine would run the 
most quietly, and that point was found to be about 7 
lbs. gauge pressure. A No. 10 spring was used. The 
horse power developed was 227.5, which multiplied by 



"a 



Vqcuu/rj 27 *l 
Joi/es fressvre nfi, 

Hep in. 



FIGURE 77. 



2, as there were two engines, would equal 455 I. H. P. 
But the rate of steam consumption, which was 
23.3 lbs. per I. H. P. per hour, was considerably 
higher than it was with the ordinary load, as when 
Fig- 75 was taken, showing that it is very poor econ- 
omy to run an engine very much below its rated 
capacity. 

Fig. 78 is from a Hamilton corliss non-condensing 
engine 32^/3 in. bore by 72 in. stroke. A No. 60 spring 
was used, the boiler pressure being 85 lbs. gauge. The 
I. H. P. was 652.2 and the steam consumption per 
I. H. P. per hour was 22.9 lbs. 



23f> 



ENGINEERING 



There are but few points about the diagram that are 
open to criticism. The compression is rather high for 
so large an engine and the steam lines should be main- 
tained more nearly horizontal up to the point of cut. 
off. 

Steam Consumption from Indicator Diagrams. In cal- 
culating the steam consumption of an engine, two very 
important factors must not be lost sight of, viz., clear- 
ance and compression. Especially is this the case in 
regard to clearance when there is little or no compres- 
sion, for the reason that the steam required to fill the 
clearance space at each stroke of the engine is prac- 




figure 78. 



tically wasted, and all of it passes into the atmosphere 
or the condensor, as the case may be, without having 
done any useful work except to merely fill the space 
devoted to clearance. On the other hand, if the 
exhaust valve is closed before the piston completes 
the return stroke, the steam then remaining in the 
cylinder will be compressed into the clearance space 
and can be deducted from the total volume which, 
without compression, would have been exhausted at 
the terminal pressure. 

Figs. 79 and 8o, which are reproductions of diagrams 
taken by the author while adjusting the valves on a 
16 x 42 in. corliss engine, will serve to graphically 



DIAGRAM ANALYSIS 



237 



illustrate this point. Fig. 79, which was the first one 
to be taken, shows no compression. The point of 
admission at A is plainly defined by the square corner 
at the extreme end of the stroke. The clearance of 



FIGURE 79. 



this engine is 4 per cent, of the volume of the piston 
displacement. The engine being 16 in. bore by 42 in. 
stroke, the piston displacement is found by the follow- 
ing calculation: Area of piston, 201.06 sq. in. x stroke, 




FIGURE 80. 



42 in. = 8444.52 cu. in. The volume of clearance 
space is equal to 8444.52 cu. in. x .04 = 337.78 cu. in., 
which divided by 1,728 = .195 cu. ft. 

By reference to Fig. 80, taken after adjusting the 



238 ENGINEERING 

valves for compression, it will be noticed that the 
steam is there compressed to 37 lbs., the compression 
curve beginning at C and ending at B. There is 
therefore compressed during each stroke a volume of 
steam equal to .195 cu. ft. at a pressure of 37 lbs. 
gauge, or 52 lbs. absolute. 

One cubic foot of steam at 52 lbs. absolute pressure 
weighs .1243 lbs., and .195 cu. ft. will weigh .1243 x 
.195 = .0242 lbs. 

The engine was running at 70 R. P. M., or 140 
strokes per minute. Thus, according to Fig. 80, the 
total weight of steam compressed and doing useful 
work during one hour, and which without compression 
would have passed out through the exhaust pipe, is 
equal to .0242 x 140 x 60 = 203.28 lbs. 

Now in order to estimate the steam consumption of 
the above engine from diagram Fig. 79, it would be 
necessary to account for all the steam occupying not 
only the volume of the piston displacement at the end 
of the stroke, but the clearance as well, for the reason, 
as before stated, that it would all be released before 
exhaust closure. This would equal 8444.52 cu. in. 
+ 337-78 cu. in = 8782.3 cu. in., which divided by 
1,728=5.08 cu. ft. each stroke, or 10.16 cu. ft. each 
revolution. 

The absolute terminal pressure of Fig. 79 is 20 lbs. 
One cubic foot of steam at this pressure weighs .0507 
lbs., and the weight of steam consumed each revolu- 
tion would therefore be 10.16 x .0507 = .515 lbs., which 
multiplied by 70 R. P. M. = 36.05 lbs. per minute, or 
2,163 l°s. P er hour. The horse power developed by 
the engine at the time was 80. Therefore the steam 
consumption per I. H. P. per hour = 2, 163 -*■ 80 = 27 
lbs. 



DIAGRAM ANALYSIS 239 

Referring again to Fig. 80 it will be remembered 
that the total weight of steam compressed during one 
hour was 203.28 lbs. The weight of steam consumed 
per hour, therefore, equals 2, 163 — 203.28 = 1959.7 lbs. 

Owing to compression, the work area of Fig. 80 is 
somewhat smaller than that of Fig. 79, amounting in 
fact to the area of the irregular figure enclosed between 
the points A, B and C. The work represented by this 
figure amounts to a very small proportion of the total 
work indicated by Fig. 79, still in order to arrive at 
correct conclusions, it should be deducted therefrom. 

Assuming the negative work to be equal to .55 horse 
power, we have 80 -.55 = 79.45 I. H. P. as the work 
represented by Fig. 80. As the total weight of steam 
consumed in one" hour was 1959.7 lbs., the steam con- 
sumption per I, H. P. per hour will be 1959.7 + 
79.45 = 24.67 lbs., a saving by compression of 2.33 lbs. 
per H. P. per hour, besides the great advantage of 
having a cushion of steam in contact with the piston at 
the termination of the stroke, thus bringing the mov- 
ing parts of the engine to rest quietly without shock 
or jar. 

The steam consumption may also be computed from 
the diagram, regardless of the dimensions of the 
cylinder or the horse power developed. The mean 
effective pressure and also the absolute terminal pres- 
sure must, however, be known. This method was 
referred to in the preceding chapter, but in the com- 
putation therein made no correction was made for 
clearance and compression. 

Having reviewed these two factors at considerable 
length it will now be in order to more fully explain 
the methods of treating diagrams when it is desired to 
make these corrections. 



240 



ENGINEERING 



First, draw vertical lines C and D, Fig. 81, at each 
end of the diagram, and perpendicular to the atmos- 
pheric line. Draw line V, representing perfect vacuum, 
14.7 lbs. below the atmospheric line, as indicated on 
the scale adapted to the diagram, which in this case is 
50 lbs. to the inch. Continue the expansion from R, 
where release begins, until it intersects line Li V, from 
which point the absolute terminal pressure can be 
measured. 

Having ascertained the terminal pressure, which for 
Fig. 81 is 30 lbs., draw line D E, which may be called 




JJ£. 



FIGURE 81. 



the consumption line for 30 lbs. The terminal 
being 30 lbs., refer to Table 10 and find in column W, 
opposite 30 in column T. P., the number 1,024.5. 
Divide this number by the M. E. P which in Fig. 81 is 
41 lbs., and the quotient, which is 24.99 lbs., is the 
uncorrected rate of steam consumption. This rate 
stands for the total consumption throughout the whole 
stroke represented on the diagram by the distance 
from D to C, which measures 3.25 in., but it is evident 
that there is a small portion of the return stroke, that' 
indicated by the distance from E to C, during which 



DIAGRAM ANALYSIS 241 

the steam compressed in the clearance space should 
not be charged to the consumption rate, but should 
be deducted therefrom. In order to do this, 
multiply the uncorrected rate by the distance from D 
to E, which is 3^ in, or 3.125 in., and divide the pro- 
duct by the distance from D to C, 3^ in., or 3.25 in. 
Thus, 24.99 x 3- I2 5 + 3- 2 5 = 2 4-03 lbs., which is the cor- 
rected rate and represents a saving by compression of 
24.99 — 24.03 = .96 lbs., or nearly 3.7 per cent. 

In many cases the terminal pressure greatly exceeds 
the compression, an illustration of which is given in 
Fig. 82 which is a reproduction of a diagram from an 



FIGURE 82. 

old Wheelock engine. It now becomes necessary to 
extend the compression curve to L, a point equidistant 
from the vacuum line with the terminal at R. The 
consumption line R. L. now becomes longer than the 
stroke line R. M., therefore the corrected rate will 
exceed the uncorrected rate by just so much; as for 
instance, terminal pressure = 34 lbs. The factor, as 
per Table 10, = 1152.26, and the M. E. P. of the diagram 
is 47 lbs. Then, 1,152.26-47 = 24.5 lbs., uncorrected 
rate; 24.5 x 3.125 in. (distance R. L.) - 3 in. (distance 
R. M.) = 25.52 lbs., corrected rate, a loss of a little 
more than one pound, or about 4 per cent. 



242 



ENGINEERING 



There is another class of diagrams very frequently 
encountered in which the terminal pressure is con- 
siderably below the compression curve, and in order to 
compute the consumption rate by the above method it 
becomes necessary to continue the compression curve 
downwards until it meets the terminal, as illustrated at 
A, Fig. 83, which is a friction diagram from a Buckeye 
engine. R is the point of release, D A represents the 
consumption line, and D C the stroke. The terminal 




FIGURE 83. 



is 8.5 lbs., and the factor for that pressure, according 
to Table 10, is 312.8. Dividing this number by the M. 
E.P., which was 7 lbs., gives 44.6 lbs. as the uncor- 
rected rate. The distance D to A, where the com- 
pression curve intersects the consumption line, is 
2.625 in., and the total length of the diagram C to 
D is 3-375 ln - Then 44.6x2.625^3.375 = 35 lbs. as 
the corrected rate. The extremely high rate is owing 
to the fact that the engine was running light, no load 
except a line of empty shafting. 



DIAGRAM ANALYSIS 243 

Theoretical Clearance. The expansion and compres- 
sion curves of a diagram are created by the expansion 
and compression of all the steam admitted during the 
stroke. This includes the steam in the clearance space 
as well as in the" cylinder proper. It is evident, 
therefore, that the volume'of the clearance is one of 
the factors controlling the form of these curves, and 
when the clearance is known a correct expansion or 
isothermal curve maybe theoretically constructed, as 
will be explained later on. Also if the actual curves, 
either expansion or compression, of a diagram assume 
an approximately correct form, the clearance, if not 
already known, may be determined theoretically from 
them; although too much confidence should not be put 
in the results as they are liable to show either too little 
or too much clearance, generally the latter, especially 
if figured from the compression curve. 

For the benefit of those who may desire to test this 
method of ascertaining the percentage of clearance of 
their engines, several illustrations will be given of its 
application to actual diagrams taken from engines in 
which the clearance was known. 

Fig. 84 is from an engine in which the clearance 
was known to be 5 per cent. As compression cuts but 
a very small figure in this diagram, the expansion 
curve alone will be utilized for obtaining the theoreti- 
cal clearance, and the process is as follows: 

Select two points, C and R, in the curve as far apart 
as possible, but be sure that they are each within the 
limits of the true curve. Thus C is located just after 
cut off takes place, and R is at a point just before 
release begins. From C draw line C D parallel with 
the atmospheric line. From D draw line D R, and 
from C draw line C E, both perpendicular to the 



244 



ENGINEERING 



atmospheric line. Then from R draw line R E, form- 
ing a rectangular parallelogram, C D R E, with two 
opposite corners, C and R, within the curve. Now 
through the other two corners, D and E, draw the 
diagonal D E, extending it downwards until it inter- 
sects the vacuum line V. From this point erect the 
vertical line V W, which is the theoretical clearance 
line. 

To prove the result proceed as follows: Measure 
the length of diagram from F to G, which in this case 




FIGURE 84. 



is 3.75 in., representing piston displacement. Next 
measure the distance from F to the clearance line V W, 
which is 3.91 in., representing piston displacement 
with volume of clearance added. Then 3.91-3-75 = 
.16, which represents volume of clearance; and . 16 x 
100 ^3.75 = 4-3 per cent., which is approximately near 
the actual clearance, which, as before stated, was 5 per 
cent. 

Fig. 85 serves to illustrate the same method applied 
to the compression curve. This diagram is a repro- 



DIAGRAM ANALYSIS 



245 



duction of one taken from the low pressure cylinder of 
a large compound condensing corliss engine in which 
the actual clearance was 2.25 per cent. Two points, G 
and H, are selected in the compression curve, and 
from them the parallelogram GHI'K is erected 
with two of its opposite corners, G and H, well within 
the limits of the curve, while through the other two 
corners, I and K, the diagonal I K C is drawn 
intersecting the vacuum line at C, thus locating the 



J 


1 










H 


I 






c 


1 






V 



FIGURE 85. 



point from which the clearance line C D can be drawn. 
The measurements in this case are as follows: 

Total length of diagram, E to F = 3.75 in. 

Distance from clearance line, DC, to F = 3.875 in. 

Volume of clearance = 3.875 — 3.75 = . 125 in. 

. 125 x 100 -*■ 3.75 = 3.33 per cent, clearance, which is 
1.08 per cent, more than the known clearance. 

However, notwithstanding the liability to error in 
many cases, still this method of computing clearance 
may often be utilized to good advantage. 

Another and more practical method of measuring 
clearance is as follows: Place the engine on the dead 
center. Remove the valve chest cover and take out 
the valve. Close the cylinder cock on that end of the 
cylinder to which the piston has been moved, leaving 



9A() ENGINEERING 

the cock on the opposite end of the cylinder open and 
disconnected from its drip pipe, so as to give an 
opportunity for catching any water that may leak past 
the piston while measuring the clearance space. Then 
having first provided a known weight of water, always 
making sure of having a little more than enough, pour 
it into the steam port until the clearance space is filled 
to a level with the valve seat. When this is done, 
weigh the water that is left and deduct it from the 
original quantity, and the remainder will be the num- 
ber of pounds of water required to fill the clearance, 
from which it is an easy matter to compute the number 
of cubic inches or cubic feet in the space devoted to 
clearance. If any water leaks past the piston during 
the operation it should be weighed and deducted from 
the total quantity poured into the port. 

In the case of an engine having the valve chest on 
the side of the cylinder it will be necessary to close 
the steam port either by blocking the valve against it 
or by fitting a piece of soft wood into it, making it 
water tight. The water can then be poured into the 
clearance space through a pipe conncted to the indi- 
cator opening in that end of the cylinder. Care should 
be exercised to allow a vent for the air to escape as it 
is displaced by the water. 

The Theoretical Expansion Curve. According to 
Boyle's law the volume of all elastic gases is inversely 
as their pressures, and steam being a gas conforms sub- 
stantially to this law; although the expansion curves 
of indicator diagrams are affected more or less by the 
loss of heat transmitted through the cylinder walls, 
and by the change in the temperature of the steam 
produced by the changes in pressure during the prog- 
ress of the stroke. The pressure generally falls more 



DIAGRAM ANALYSIS 



247 



rapidly during the first part of the stroke, and less 
rapidly during the last portion than it should in order 
to conform strictly to the above law, and the terminal 
pressure usually is greater than it should be to agree 
with the ratio of expansion. But this fullness of the' 
expansion curve of the diagram near the end compen- 
sates in a measure for the too rapid fall near the begin- 
ning of the stroke. Therefore, if the engine is in 
fairly good condition with the valves properly adjusted 
and not leaking, and the piston rings are steam tight, 



Jj 


) 


I 


1 


«--— ^"^ 








1 -=4 









Af 



JO C$ A 



it may be assumed that the expansion of the steam in 
the cylinder takes place according to Boyle's law and 
it is found that the expansion curve drawn by the indi- 
cator practically coincides with a hyperbolic curve 
constructed according to that law. 

Fig. 86 graphically illustrates the application of the 
hyperbolic law to the expansion of gases. The hori- 
zontal lines represent volumes and the vertical lines 
represent pressures. The base line, A F, represents 
the full stroke of a piston in the cylinder of an engine, 



248 ENGINEERING 

and the vertical line A I represents the pressure of 
the steam at the commencement of the stroke. 

Suppose there is no clearance and that the steam has 
been admitted up to point H when it is cut off. The 
rectangle A B H I is the product of the pressure mul- 
tiplied by the volume of the steam thus admitted. 
When the piston has traveled from A to C the volume 
of the steam has been doubled and the pressure C L 
has been reduced to just one-half what it was at A I, 
but the area of the rectangle A C L M is equal to the 
area of the initial rectangle, and, as before, is the pro- 
duct of the pressure C L multiplied by the volume A C. 
As the piston travels still farther, as from A to D, the 
steam is expanded to four volumes while the pressure 
at D K will only be one-fourth that of the initial 
pressure; but the new rectangle A D K N is still equal 
in area to either of the others, A B H I or A C L M. 

'The same law applies to each of the remaining rect- 
angles; A E G O representing five volumes and one- 
fifth of the initial pressure, and A F R P representing 
six times the initial volume and one-sixth of the initial 
pressure, but each having the same area as the initial 
rectangle A B H I. Now the area of the rectangle 
A B H I represents the work done by the steam up to 
the point of cut off, and the area of the hyperbolic fig- 
ure enclosed by the lines B H R F represents the work 
done by the expansion of the steam after cut off 
occurs. This area and the amount of work it repre- 
sents may be computed by means of the known rela- 
tions of hyperbolic surfaces with their base lines; as 
for instance, if the base lines A B, A C, A D, etc., 
extend in geometrical ratio, as r, 2, 4, 8, 16, etc., the 
successive areas, B H L C, B H K D, B H G E, etc., 
increase in arithmetical ratio, as 1, 2, 3, 4, etc. 



DIAGRAM ANALYSIS 



249 



On the principles of common logarithms, which 
represent in arithmetical ratio natural numbers in 
geometrical ratio, tables of hyperbolic logarithms have 
been computed for the purpose of facilitating the cal- 
culation of areas of work due to different degrees of 
expansion. Such a table is given elsewhere in this 
book, and in Chapter IX is described the method of 
calculating the M. E. P. by this means. 

A theoretical curve may be constructed conjointly 
with the actual expansion curve of a diagram by first 
locating the clearance and vacuum lines and then pur- 




figure 87. 



suing the method illustrated by Fig. 87. A curve so 
produced is called an isothermal curve, meaning a 
curve of the same temperature. 

Referring to Fig. 87, suppose, first, that it is desired 
to ascertain how near the expansion curve of the dia- 
gram coincides with the isothermal curve, at or near 
the point of cut off. Select point R near where 
release begins, but still well within the expansion 
curve. From this point draw the vertical line, R T, 
parallel with the clearance line, V S. Then draw the 
horizontal line, S T, parallel with the atmospb^'c line, 



250 ENGINEERING 

and at such a height above it as will equal the boiler 
pressure as measured by the scale adapted to the dia- 
gram; such measurement to be made "from the atmos- 
pheric line to correspond with the gauge pressure. 
From T draw the diagonal T V, and from R draw the 
horizontal line R D parallel with the atmospheric line. 
From D, where this line intersects T V, erect the 
perpendicular D E, thus forming the parallelogram 
R D E T, and as line T V passes through two of its 
opposite angles and meets the junction of the clear- 
ance and vacuum lines, the other two angles, R and 
E, will be in the theoretical curve, and R being the 
starting point, it is obvious that this curve must pass 
through E, which would be the theoretical point of 
cut off on the steam line S T. 

Two important points in the theoretical curve have 
now been located, viz., E as the cut off, and R as the 
point of release. In order to obtain intermediate 
points, draw any desired number of lines downward 
from points in S T, as I, 2, 3, 4, 5, etc., and continue 
them downwards far enough to be sure that they will 
meet the intended curve, and from the same points in 
S T draw diagonals 1 V, 2 V, 3 V, 4 V, 5 V, etc., all 
to converge accurately at V. From the intersection of 
these diagonals with D E draw horizontal lines paral- 
lel with V V, and the points of junction of these lines 
with the vertical lines will be points in the theoretical 
curve. It will now be an easy matter to trace the 
curve through these points. If, on the other hand, it 
be desired to compare the curves toward the exhaust 
end of the diagram, draw lines E D and E T, Fig. 88, 
also T R, locating R near where release commences, 
after which draw line R D, completing the parallelo- 
gram E T R D, fixing R as a point in the theoretical 



DIAGRAM ANALYSIS 



251 



curve started at E. After drawing the diagonal T V, 
proceed in the same manner as before to locate the 
intermediate points. 

It will be observed that in order to ascertain the 
performance of the steam near the beginning of the 
stroke, the starting point of the isothermal curve must 
be near the point of release, and conversely, if the 
starting point of the curve is located near the point of 
cut off and coincident with the actual curve, the test 
will apply towards the end of the stroke. It is not to 
be expected that the expansion curve of any diagram 
taken in practice will conform strictly to the lines of 




figure 88. 



the isothermal curve, especially towards the latter end 
of the stroke, owing to the reevaporation of water 
resulting from the condensation of steam which was 
retained in the cylinder by the closing of the exhaust 
valve. This reevaporation commences just as soon as 
the temperature of the steam, owing to reduction of 
pressure due to expansion, falls below the temperature 
of the cylinder walls, and it continues at an increasing- 
rate until release occurs. The tendency of this 
reevaporation or generation of steam within the 
cylinder during the latter portion of the stroke is to 



ENGINEERING 



raise the terminal pressure considerably above what it 
would be if true isothermal expansion took place. 
The terminal pressure may also be augmented by a 
leaky steam valve, while, on the other hand a leaky 
piston would cause a lowering of the terminal and an 
increase in the back pressure. 

The Adiabatic Curve. If it were possible to so pro- 
tect or insulate the cylinder of a steam engine that 
there would be absolutely no transmission of heat 
either to or from the steam during expansion, a true 
adiabatic curve or "curve of no transmission" might 



r 




Ic 




s 




t -^~~ 






/ 


/ 




7 




' / 


u 




/ / 












.ss 




// 






ss 






~<^ 












^^z^-~ 




H 


-js-s- 51 """^ 


-2L 


c 


J 


A 


V 


V 



be obtained. The closer the actual expansion curve 
of a diagram conforms to such a curve, the higher will 
be the efficiency of the engine as a machine for con- 
verting heat into work. 

Fig. 89 illustrates a method of figuring a curve 
which, while not strictly adiabatic, will be near 
enough for all practical purposes, while at the same 
time it will give the student an opportunity to study 
the laws governing the expansion of saturated steam. 

To draw the curve, first locate the clearance anc 
vacuum lines V S and V V. Next locate point R in 



DIAGRAM ANALYSIS 253 

the expansion curve near where release begins, making 
this the starting point, and also the point of coinci- 
dence of the expansion curve with the adiabatic curve. 
The other points in the curve are located from the 
volumes of steam at different pressures during expan- 
sion; the pressures being measured from the line of 
perfect vacuum, and the volumes from the clearance 
line. 

The absolute pressure at R, Fig. 89, is 26 lbs. From 
point R erect the perpendicular R T. Also draw hori- 
zontal line R 26 parallel with the vacuum line and at a 
height equal to 26 lbs. above vacuum line V V, as 
shown by the scale, which in this case was 40. The 
length of line R 26, measured from R to the clearance 
line, is 3 T V in., or 3.0625 in. By reference to Table 5 
it will be seen that the volume of steam at 26 lbs. abso- 
lute, as compared with water at 39 , is 962. Now if 
the length of line R 26 be divided by this volume, and 
the quotient multiplied by each of the volumes of the 
other pressures represented at points 30, 35, 40, 45, 
etc., up to the initial pressure, the products will be 
the respective distances from the clearance line of 
points in the adiabatic curve. These points can be 
marked on the horizontal lines drawn from the 
clearance line to line R T. 

Starting with line R 26, it has been noted that its 
length is 3.0625 in., and that the volume was 962. 
3.0625-962^.003. Then the volume of steam at 30 
lbs. is 841, which being multiplied by .003 = 2.5 in., the 
length of line 30. Next the volume at 35 lbs. = 728. 
Multiplying this volume by .003 = 2.1 in., length of 
line 35, and so in like manner for each of the other 
points. 

The process involves considerable figuring and care- 



254 ENGINEERING 

ful and accurate measurements, which should be made 
with a steel rule with decimal graduations. It is not 
expected that the cut Fig. 89 will be found accurate 
enough in its measurements to serve as a standard; it 
being intended only to serve as an illustration of the 
process. The diagram from which the illustration was 
drawn was taken from a 600 H. P. engine situated 
some 200 ft. from the boilers, and there was a con- 
siderable cooling of the steam by the time it reached 
the engine, the effect of which is apparent. The 
curve produced by the measurements is shown by the 
broken line. The process can be applied to any dia- 
gram. 

Power Calculations. The area of the piston (minus 
one-half the area of rod) multiplied by the M. E. P., as 
shown by the diagram, and this product multiplied by 
the number of feet traveled by the piston per minute 
(piston speed) will, give the number of foot pounds of 
work done by the engine each minute, and if this pro- 
duct be divided by 33,000, the quotient will be the 
indicated horse power (I. H. P.) developed by the 
engine. 

Therefore one of the first requisites in power calcu- 
lations is to ascertain the M. E. P. Beginning with 
the most simple, though only approximately correct, 
method of obtaining the average pressure, as illus- 
trated by Fig. 90, draw line A B touching at A and 
cutting the diagram in such manner that the space D 
above it will equal in area spaces C and E taken 
together, as nearly as can be estimated* by the eye. 
Then with the scale measure the pressure along the 
line F G at the middle of the diagram, which will be 
the M. E. P. 

The process is based upon the theory that the 



DIAGRAM ANALYSIS 



255 



average width of any tapering figure is its width at 
the middle of its length. This method should not be 
relied upon as accurate, but is convenient at times 
when it is desired to make a rough estimate of the 
horse power of an engine. 

Figuring the M. E. P. by Ordinates. This is a very 
common method and one which can be relied upon to 
give accurate results, provided care is exercised in its 
use. 

The process consists in drawing any convenient 



P 

FIGURE 90. 



number of vertical lines perpendicular to the atmos- 
pheric, line across the face of the diagram, spacing 
them equally, with the exception of the two end 
spaces, which should be one-half the width of the 
others, for the reason that the ordinates stand for the 
centers of equal spaces, as for instance, line I, Fig. 91, 
stands for that portion of the diagram from the end to 
the middle of the space between it and line 2. Again, 
line 2 stands for the remaining half of the second 
space and the first half of the third, and so on. This 



&5(i 



ENGINEERING 



is an important matter, and should be thoroughly under- 
stood, because if the spaces are all made of -equal 
width, and measurements are taken on the ordinates, 
the results will be incorrect, especially in the case of 
high initial pressure and early cut off, following which 
the steam undergoes great changes. 

If the spaces are all made equal, the measurements 
will require to be taken in the middle of them, and 
errors are liable to occur, whereas if spaced as before 
described, the measurements can be made on the 



CrqnKEntL 



¥1 

JS 

S 

'9 
to. I 




167./ + /0 - zL. 7/ {^ fl.FP 

trrjr. m.£.p 



FIGURE 91. 



ordinates, which is much more convenient and will 
insure correct results. Any number of ordinates can 
be drawn, but ten is the most convenient and is amply 
sufficient, except in case the diagram is excessively 
long. For spacing the ordinates, dividers may be 
used, or a parallel ruler may be procured from the 
makers of the indicator; but one of the most con- 
venient and easily procurable instruments for this pur- 
pose is a common two-foot rule, and the method of 
using it is illustrated in Fig. 91. 

First draw vertical lines at each end of the diagram, 



DIAGRAM ANALYSTS 2.57 

perpendicular to the atmospheric line and extending 
downwards to the vacuum line, or below it if neces- 
sary, in order to have a point on which to lay the 
rule. In Fig. 91 points A and B are found to be the 
most convenient. Now lay the rule diagonally across 
the diagram, touching at A and B, and the distance 
will be found to be 3% in., or 60 sixteenths. 

Suppose it be desired to draw 10 ordinates. Divide 
63 by 10, which will give 6 sixteenths, or 3/s in. as the 
width of the spaces, but as the two end spaces are to 
be one-half the width of. the others, there will be 11 
spaces altogether, the two outer ones having a width 
equal to one-half of ^ or T \. Now apply the rule 
again in the same manner, touching at points A and B, 
and with a sharp pointed pencil begin at A and mark 
the location of the first ordinate according to the rule, 
at a distance of y\- from the end. "Then 3/s from this 
mark make another one, which will locate the second 
ordinate, and proceed in like manner to locate the 
others. The last two or three marks generally come 
below the diagram, and if the diagram be taken from a 
condensing engine it may be necessary to tack it on to 
a larger sheet of paper in order to get these points. 
Having correctly located the ordinates, they may now 
be drawn perpendicular to the atmospheric line or 
vacuum line, either of which will answer. 

It should be noted that, owing to the diagonal posi- 
tion of the rule with relation to the atmospheric line, 
the spaces are not of the actual width as described by 
the rule, but this is unimportant, so long as they are of 
a uniform width. This method can be applied to any 
diagram, no matter what its length may be, and point 
B may be located at any distance below the atmos- 
pheric or vacuum lines, wherever it is the most con- 



258 ENGINEERING 

venient for the subdivisions on the rule, sixteenths, 
eighths, etc., so long as it is in line with the e'nd of 
the diagram. Having thus drawn the ordinates, the 
M. E. P. may.be found by measuring the pressure 
expressed by each one, using for this purpose the 
scale adapted to the spring used, adding all together 
and dividing by the number of ordinates which will 
give the average pressure. 

Referring to Fig. 91, begin with ordinate No. 1 on 
the diagram, from the head end of the cylinder. In 
this case a 40 spring was used. Lay the scale on the 
ordinate with the zero mark where it intersects the 
compression curve. The pressure is seen to be 49 lbs. 
Set this down at that end of the card and measure the 
pressure along ordinate No. 2, which is 55 lbs. Pro- 
ceed in this manner to measure all the ordinates, 
placing the resulting figures in a column, after which 
add them together and divide by 10. The result is 
26.71 lbs., which is the mean forward pressure (M. 
F. P.). To obtain the mean effective pressure, deduct 
the back pressure, which is represented by the distance 
of the exhaust line of the diagram above the atmos- 
pheric line in a non-condensing engine, and in a con- 
densing engine the back pressure is measured from the 
line of perfect vacuum, 14.7 lbs., according to the scale 
below the atmospheric line. 

In Fig. 91 the back pressure is found to be 3 lbs. 
Therefore the M. E. P. of the head end will be 
26.71 - 3 = 23.71 lbs. On the crank end the M. F. P. 
is 27.23 lbs, and 27.23 - 3 - 24.23 lbs. = M. E. P. The 
average effective pressure on the piston, therefore, will 
be 23.71 + 24.23 * 2 = 23.97 lb s - 

Unless great care is exercised in the measurements, 
errors are liable to occur in applying this method, 



DIAGRAM ANALYSIS 259 

especially with scales representing high pressures, as 
60, 80, etc. The most convenient and reliable method 
is to take a narrow strip of paper of sufficient length, 
and starting at one end, apply its edge to each ordinate 
in succession and mark their lengths on it consecu- 
tively with the point of a knife blade or a sharp pen- 
cil, Having thus marked on the paper the total length 
of all the ordinates, ascertain the number of inches and 
fractions of an inch thereon, the fractions to be 
expressed decimally, and divide by the number of 
ordinates. The quotient will be the average height of 
the diagram, and as the scale expresses the number of 
pounds pressure for each inch or fraction of an inch in 
height, if the average height of the diagram be multi- 
plied by the number of the scale, the product will be 
the M. F. P. 

Referring again to Fig. 91, if the lengths of the 
ordinates drawn on the head end diagram be measured, 
their sum will be found to be 6 T 8 ¥ or 6.666 in. Divid- 
ing this by 10 gives .666 in. as the average height. 
The mean forward pressure will then be as follows: 
.666 x 40 = 26.64 lbs., or oractically the same as found 
by the other method. 

Fig. 92 illustrates a type of diagram frequently met 
with, and one which requires somewhat different 
treatment in estimating the power developed. It will 
be noticed that, owing to light load and early cut off, 
the expansion curve drops considerably below the 
atmospheric line, notwithstanding that the engine 
from which this diagram was taken is a non-con- 
densing engine. When release occurs at R, and the 
exhaust side of the piston is exposed to the atmos- 
phere, the pressure immediately rises to a point equal 
to, or slightly above, that of the atmosphere. 



260 



ENGINEERING 



Fig. 92 was taken during a series of experiments 
made by the author for the purpose of ascertaining the 
friction of shafting and machinery, and the engine it 
was obtained from is a Buckeye 24 x 48 in. The 
boiler pressure at the time was only 40 lbs., and a No. 
20 spring was used. The ordinates are drawn accord- 
ing to the method illustrated in Fig. 91. By placing 
the rule on points A and B, the distance between 
those two points is found to be 3^8 in., or 58 sixteenths. 
Dividing this by 10 gives 5.8 sixteenths, or nearly ^ 






Sp'typ 




FIGURE 92. 



in., as the width of the spaces; the two end spaces 
being one-half of this, or T \ in. wide. The first five 
ordinates, counting from A, express forward pressure, 
represented by the arrows. The remaining five ordi- 
nates, counting from B, express counter or back pres- 
sure, represented by the arrows pointing in the 
opposite direction. Measuring the pressures along 
the first five ordinates, and adding them together, 
gives 63.1 lbs., which divided by 5 gives 12.65 ^s. as 
the mean forward pressure (M. F. P.). 



DIAGRAM ANALYSIS 



261 



Then figuring up the counter pressure in the same 
manner on the other five ordinates, beginning at B, 




COFFIN AVERAGER OR PLANIMETER. 

the result is 4.25 lbs. The M. E. P. therefore will be 
12.65 ~4- 2 5 = 8.4 lbs. 

Obtaining the M. E. P. with the Planimeter. The area 
of the diagram represents the actual work done by the 



262 ENGINEERING 

steam acting upon the piston. In a non-condensing 
engine the lower or exhaust line of the diagram must 
be either coincident with or slightly above the atmos- 
pheric line in order to express positive work. Any 
deviation of this line, either above or below the atmos- 
pheric line, represents counter pressure, the amount of 
which may be ascertained by measurements with the 
scale, and should be deducted from the mean forward 
pressure. 

On the other hand, the exhaust line of a diagram 
from a condensing engine falls more or less below the 
atmospheric line, according to the degree of vacuum 
maintained, and the nearer this line approaches the 
line of perfect vacuum, as drawn by the scale, 14.7 lbs. 
below the atmospheric line, the less will be the counter 
pressure, which in this case is expressed by the dis- 
tance the exhaust line is above that of perfect vacuum. 

The prime requisite therefore in making power cal- 
culations from indicator diagrams is to obtain the 
average height or width of the diagram, supposing it 
were reduced to a plain parallelogram instead of the 
irregular figure which it is. 

The planimeter, Fig. 93, is an instrument which will 
accurately measure the area of any plane surface, no 
matter how irregular the outline or boundary line is, 
and it is particularly adapted, for measuring the areas 
of indicator diagrams, and in cases where there are 
many diagrams to work up, it is a very convenient 
instrument and saves much time and mental effort. In 
fact, the planimeter has of late years become an almost 
indispensable adjunct of the indicator. It shows at 
once the area of the diagram in square inches and 
decimal fractions of a square inch, and when the area 
is thus known it is an easy matter to obtain the aver- 



DIAGRAM ANALYSIS 



263 



age height by simply dividing the area in inches by 
the length of the diagram in inches. Having ascer- 
tained the average height of the diagram in inches or 
fractions of an inch the mean or average pressure is 
found by multiplying the height by the scale. Or the 
process may be made still more simple by first multi- 
plying the area, as shown by the planimeter in square 




figure 93. 



inches and decimals of an inch, by the scale, and 
dividing the product by the length of the diagram in 
inches. The result will be the same as before, and 
troublesome fractions will be avoided. 

Questions 
i. What advantage is gained by placing the valves 
of a corliss engine in the cylinder head? 



264 ENGINEERING 

2. What two important factors must be considered 
in calculating the steam consumption of an engine? 

3. What advantage, in an economical way, is gained 
by compression? 

4. How is the piston displacement of an engine 
ascertained? 

5. How is the steam consumption per horse power 
per hour calculated? (See Figs. 79 and 80.) 

6. What effect does compression have upon the work 
area of an indicator diagram? (See Fig. 80.) 

7. How can the steam consumption, as shown by 
the diagram, be corrected for clearance and compres- 
sion? (See Figs. 81, 82 and 83.) 

8. What do the expansion and compression curves 
of a diagram show? (See theoretical clearance.) 

9. If the clearance of an engine is not known, how 
may it be determined theoretically from an indicator 
diagram? (See Figs. 84 and 85.) 

10. What other method may be employed to ascer- 
tain the clearance? 

11. What is Boyle's law for gases? 

12. Is steam a gas? 

13. What is a hyperbolic curve? (See Fig. 86.) 

14. How may a theoretical curve be constructed 
from an indicator diagram? (See Fig. 87.) 

15. What effect does reevaporation have upon the 
expansion curve? 

16. When does reevaporation take place within the 
cylinder? 

17. How does a leaky steam valve affect the ter- 
minal pressure? 

18. If the piston rings leak, what is the result? 

19. W T hat is an adiabatic curve, and what conditions 
are necessary in order to produce it? 



DIAGRAM ANALYSIS °265 

20. What is the rule for computing the horse power 
developed by an engine? 

21. What important factor is necessary in all power 
calculations? 

22. How may the M. E. P. be found? (See Figs. 
91 and 92.) 

23. What does the area of the diagram represent? 

24. In a diagram from a non-condensing engine, 
where should the exhaust line be? 

25. If the exhaust line of a diagram is above the 
atmospheric line, what does it show? 

26. Where should the exhaust line of a diagram from 
a condensing engine be? 

27. How is the M. E. P. ascertained by the plani- 
meter? 



CHAPTER XI 

ENGINE OPERATION 

Engine operation — Simple engines — Compound engines — Con- 
densing and non-condensing engines — Condensers — Surface 
and jet condensers — Starting a condensing engine — Rules for 
estimating quantity of condensing water required — The gov- 
ernor — Speed regulation — How to keep a governor in good 
working condition — Lubrication of an engine — Running 
"over" or "under" — Oiling the bottom guide on horizontal 
engines — Oiling the crank pin and main bearings — Shaft gov- 
ernors—Keying up an engine — What to do with a hot pillow 
block — Feed water heaters — Economy of using exhaust steam 
for heating feed water — Changing the speed of an engine. 

The following general suggestions regarding the 
operation of engines are made with the object in view 




CROSS COMPOUND DIRECT CONNECTED . CORLISS ENGINE, ALLIS 
CHALMERS CO. 

of assisting young engineers or those whose experience 
has been limited to one or two types of engines. 

In many cases a young man starts in as a fireman in 
266 



ENGINE OPERATION 267 

a certain plant, and by industry and a strict devotion 
to duty becomes able in course of time to handle not 
only the boilers successfully, but is at times required 
to run the engine in the absence of the engineer. He 
thus acquires the ability to operate that particular 
engine, while at the same time he may be compar- 
atively ignorant of the peculiarities of other types. 
Or an engineer may have had years of experience with 
simple non-condensing engines, but if called upon to 
operate a compound condensing engine, he would find 
that he had a great deal to learn. 



TANDEM COMPOUND ENGINE, BUCKEYE ENGINE CO. 

Engines may be divided into two general classes, 
viz., simple and compound. 

A simple engine may be either condensing or non- 
condensing, but its leading characteristic is, that the 
steam is used in but one cylinder, and from thence it is 
exhausted either into the atmosphere or into a con- 
denser. 

A compound engine is one in which the steam is 
made to do work in two or more cylinders before it is 
allowed to exhaust, and this class of engine may be 
either condensing- or non-condensing;. 



ENGINEERING 




*:':tf% 




ENGINE OPERATION 



2G9 



In a non-condensing engine the pressure of the 
atmosphere, amounting to 14.7 lbs. per square inch at 
sea level, is constantly in resistance to the motion of 



EXHAUST 
INLET 




KNOWLES JET CONDENSER. 



the piston. Therefore the exhaust pressure cannot 
fall below the atmospheric pressure, and is generally 
from two to five pounds above it, caused by the resist- 
ance of bends and turns in the exhaust pipe, or other 



270 ENGINEERING 

causes which tend to retard the free passage of the 
steam. 

The advantage, from an economical point of view, 
of exhausting the steam into a condenser in which a 
vacuum is maintained, is fully set forth in Chapter 
VIII. on Definitions. (See" Vacuum.) 

Condensers are of two classes, viz., jet condensers 
and surface condensers. 

In a jet condenser the steam is exhausted into an 
air-tight iron vessel of any convenient shape, gener- 
ally cylindrical and of suitable size, and is there con- 
densed by coming in contact with a jet of cold water, 
admitted in the form of a spray. The air pump, which 
also maintains a vacuum in the condenser, draws this 
water, together with the condensed steam, away from 
the condenser. 

The surface condenser, like the jet condenser, con- 
sists of an air-tight iron vessel, either cylindrical or 
rectangular in shape, but unlike the jet condenser, it 
is fitted with a large number of brass or copper tubes 
of small diameter, through which cold water is forced 
by a pump, called a circulating pump. A vacuum is 
also maintained in the body of the condenser by the 
air pump, and the steam exhausting into this is con- 
densed by coming in contact with the cool surface of 
the tubes. Or, as is often the case, the exhaust steam 
passes through the tubes in place of around them, and 
the condensing water is forced into and through the 
body of the condenser, the vacuum in this case being 
maintained in the tubes. Owing to the fact that in a 
surface condenser the steam does not mix with the 
water, a larger quantity of condensing water is required 
than in a jet condenser, but on the other hand, an 
advantage is gained by having the pure water of con- 



ENGINE OPERATION 



271 



densation; in other words, the condensed steam, which 
may be returned to the boilers along with the regular 
feed water supply, and will greatly aid in preventing 
the formation of scale, while the water of condensation 
as it comes from a jet condenser, being mixed with 
oil and other impurities, is not, as a rule, suitable to 
be fed to boilers. 

There are many different types of jet condensing 




WORTHINGTON SURFACE CONDENSER, WITH AIR AND CIRCU- 
LATING PUMP- 



apparatus, in some of which no air pump is used; their 
action being based somewhat upon the principle of the 
injection used for feeding boilers. In this type of jet 
condenser the supply of condensing water is drawn from 
outside pressure, either from an overhead tank or other 
source, and passing into an annular enlargement of the 
exhaust pipe, is discharged downwards in the form of 
a cylindrical sheet of water into a nozzle which gradu- 
ally contracts. The exhaust steam, entering at the 



272 



ENGINEERING 



same time, is condensed, and the contracting neck of 
the cone shaped nozzle gradually brings the water to a 
solid jet, and it rushes through the nozzle with a veloc- 
ity sufficient to create a vacuum. This type of con- 
denser can only be used where the discharge pipe has 
a free outlet. 

The jet condenser with air pump attached is the 
most reliable as well as econom- 
ical for general purposes, for the 
reason that with this type the sup- 
ply of condensing water may be 
drawn from a well or other source 
lower than the level of the con- 
denser. These condensers are also 
generally fitted with a "force in- 
"ection," as it is called, which is 
simply a connection between the 
condenser and water main or tank, 
for the purpose of letting cold water 
into the condenser to condense the 
exhaust steam when starting the 
engine, and thus aid in forming a 
vacuum. When a good vacuum has 
been established and the engine is 
running up to speed, the force injection may be shut 
off, and the water will flow into the condenser from 
the well by suction. The above refers to engines in 
which the air pump receives its motion directly from 
the engine. 

Another type of jet condensing apparatus is the 
independent air pump and condenser, which is still 
better, for the reason that the air pump, which is sim- 
ply an ordinary double acting steam pump, may be 
started independently of the engine, and, in fact, 




SIPHON CONDENSER. 



ENGINE OPERATION 273 

before the engine is started, thus creating a vacuum in 
the condenser, and greatly facilitating the starting of 
the engine. Another great advantage in the inde- 
pendent condensing apparatus is that there is not so 
much danger of the water backing up into the cylinder 
in case of a sudden shut down of the engine, because 
the air pump may be kept in operation, thus relieving 
the condenser of water; whereas, if the air pump gets 
its motion from the engine, it will of course stop when 
the engine stops, and unless the injection water is shut 
off immediately after closing the throttle there is 
great danger of the cylinder becoming flooded with 
water, resulting very often in a broken cylinder head, 
or a bent piston rod. 

The quantity of water required to condense the 
exhaust steam of an engine is determined by three 
factors: First, the density, temperature and volume of 
the steam to be condensed in a given time; second; 
the temperature of the overflow or discharge, and 
third, the temperature of the injection water. For 
instance, the temperature of the injection water may 
be 35 in the winter and 70 ° in the summer. Or it 
may be desired to keep the overflow at as high a tem- 
perature as possible for the purpose of feeding the 
boilers. Again, the pressure, and consequently the 
temperature of the exhaust steam as it enters the con- 
denser, varies with different engines, and often with 
the same engine, according as the load is light or 
heavy. Therefore the only accurate method of esti- 
mating the amount of condensing water required per 
minute or per hour, under any and all conditions, is to 
first ascertain the weight of water required to con- 
dense one pound weight of steam at the temperature 
and pressure at which the steam is being exhausted. 



274 ENGINEERING 

In these calculations the total heat in the steam must 
be considered. This means .not only the sensible heat, 
but the latent heat also. 

The formula for solving the above problem may be 

FT — T 

expressed as follows: ~ — ~ = W, in which 

H = total heat in the steam, 
T = temperature of the overflow, 
I = temperature of the injection water, 

W = weight of water required to condense one pound 
weight of steam. 

To illustrate, suppose the absolute pressure of the 
exhaust, as shown by the indicator diagram, is y lbs. 
Referring to Table 5, it will be seen that the total heat 
in steam at 7 lbs. absolute is 1 135.9 heat units. 
Assume the temperature of the overflow to be no°, 
which is as high as is consistent with a good vacuum 
Now the total heat to be absorbed from each pound 
weight of steam in this case would be 1135.9—110 = 
1025.9 B. T. U. 

Suppose the temperature of the condensing water to 
be 55 and the temperature of the overflow being uo°, 
there will be no° — 55 = 55 of heat absorbed by each 
pound of water passing into and through the con- 
denser, and the number of pounds of water required to 
condense one pound weight of steam under the above 
conditions will equal the number of times 55 is con- 
tained in 1025.9. Expressed in plain figures the cal- 
culation is "nHl™ = 18.65 lbs. 

In order to ascertain the quantity of condensing 
water required per horse power per hour, it is only 
necessary to know the number of pounds weight of 
steam consumed by the engine per horse power per 
hour, as shown by the indicator diagram, and multiply 



ENGINE OPERATION 275 

this by the weight of condensing water required per 
pound of steam, as found by the above solution. 

Thus, suppose the steam consumption of the engine 
to be 17 lbs. per I. H. P. per hour. Then 17 x 18.65 
= 317.05 lbs. per hour, which reduced to gallons = 38.2 
gals. 

Or, if the steam consumption is not known, and the 
weight only of condensing water required per hour is 
desired, regardless of the horse power developed by 
the engine, it will be necessary, first, to estimate the 
total volume of steam exhausted per hour and calcu- 
late its weight from its known pressure. 

Thus, assume the engine to be 24x48 in., and the 
R. P..M. to be 80. Then the piston displacement will 
equal area of piston less one-half area of rod multi- 
plied by length of stroke. Referring to Table 9, the 
area of a circle 24 in. in diameter = 452.39 sq. in. 
Suppose the piston rod to be 4.5 in. in diameter, its 
area, according to Table 9, is 15.904 sq. in., one-half 
of which = 7.952 sq. in. The effective area of the pis- 
ton now becomes 452.39 — 7.952 = 444.43 sq. in., and 
the piston displacement equals 444.43 x 48 = 21332.64 
cu. in. Dividing this by 1728 (number of cubic inches 
in a cubic foot) gives 12.34 cu. ft. of piston displace- 
ment. The total volume of steam exhausted per min- 
ute, therefore, will be 12.34 x 2 x 80 = 1974.4 cu. ft. 

The absolute pressure of the exhaust may again be 
assumed to be 7 lbs. per square inch. Referring to 
Table 5, the weight of one cubic foot of steam at 7 
lbs. absolute is .0189 lbs., and the total weight of steam 
exhausted per minute, therefore, would be 1974.4 x 
.0189 = 37.3 lbs., and if 18.65 lbs. water is required to 
condense one pound of steam, the quantity required 
per minute would be 37.3 x 18.65=695.8 lbs., or per 



27G 



ENGINEERING 



hour, 41748 lbs., equal to 5029 gals. This is at the. 
rate of 8.7 lbs., or a little more than one gallon per 
revolution for a 24 x 48 in. simple condensing engine. 
The Governor. The proper regulation of speed is a 
very important point in the operation of engines, and 
in order to attain this most desirable object, due atten- 
tion must be paid to the governor. 
If it be a throttling governor (see 
Chapter VIII, on Definitions), care 
should be taken to not pack the 
small valve stem too tight, nor allow 
the packing to become hard from 
long usage. The packing nut should 
be left loose enough to allow a 
slight leakage of steam past the 
stem. This will keep it lubricated 
and the slightest variation of the 
governor balls will be transmitted 
to the valve, and the speed will be 
regular. 

If the engine has an automatic 
cut off mechanism actuated by a fly 
ball governor, it is obvious that all 
the moving parts of the governor 
should work with as little friction as possible. Good 
oil and enough of it should be used. Particular atten- 
tion should be paid to the dash pot connected with the 
governor, the object of which is to regulate the varia- 
tions of the governor and prevent a jerky movement. 
It often happens, especially with new engines, that 
the small piston in the dash pot fits too snug, and the 
consequence is that it sticks; causing the governor to 
be slow in responding to changes in the speed of the 
engine. 




PICKERING HORI- 
ZONTAL GOVERNOR 



ENGTNE OPERATION 



277 



It is a good plan sometimes to take the dash pot pis- 
ton out, and putting it in a lathe, reduce its diameter 
slightly, and also round off the sharp edges. The oil 
used in the dash pot should not be allowed to become 
gummy by being used too long without changing it for 
fresh oil. 

Lubrication. The proper lubrication of all the work- 
ing parts of an engine is a matter of prime importance, 




DOUBLE CONNECTION LUBRICATOR. 



not only in prolonging the life of the engine, but in 
reducing friction, and thus increasing efficiency. 
Various types of lubricators have been devised for 
introducing oil into the valve chest and cylinder, but 
probably the most reliable and easily managed appa- 
ratus for this purpose is a good oil pump worked by 
the engine itself, for the reason that it is positive and 
the flow of oil is not easily affected by changes in 



278 



ENGINEERING 



temperature. In the case of large horizontal engines 
especially, it is good practice to introduce a little 
graphite along with the cylinder oil once or twice a 
day. 

In many cases trouble is experienced with the bot- 




f^s* 



FIGURE 94. 



torn guides of horizontal engines, especially if the 
engine "runs over," as illustrated by Figs. 94 and 95, 
where it will be seen that in addition to the weight of 
the crosshead, the thrust or pressure consequent upon 
the pull, Fig. 94, and push, Fig, 95, also comes upon 
the bottom guide both with the inward and outward 




figure 95. 



strokes; whereas with an engine "running under," the 
thrust is just in the opposite direction, and the pres- 
sure comes upon the top guide. 

The best method of lubricating the lower guide of a 
horizontal engine is to drill through from the under- 



ENGINE OPERATION 



279 



side at a point near the center of the guide, and con- 
nect a small size pipe, ^ or ^ in., to which an oil or 
grease cup can be attached. The oil thus forced up 
from beneath will serve a much better purpose than if 
dropped on the guide, to be instantly scraped off by 
the crosshead. 

One of the best devices for oiling fhe crank pin is 
the center oiler, illustrated in Fig. 96. An oil hole is 
drilled along the center line of the pin to a point about 
midway of its length, and another hole from the 




figure 96. 



wearing surface of the pin at right angles to the first 
hole. The two holes meet at the center of the pin 
and form a route by which the oil is conducted to the 
point where it is most needed. The hole at the outer 
end of the pin is enlarged and threaded to receive the 
oil pipe, one end of which is connected to the pin by 
means of a short nipple and elbow, while the other 
end is in line with the center of the main shaft and 
remains in that position while the crank revolves. 
The oil is fed into this end of the pipe through an 



280 ENGINEERING 

elbow or hollow ball screwed to the end of the pipe, 
and the supply may be regulated at will by the engi- 
neer, as the cup is at all times under his control. 

The pillow block or main bearing of an engine 
demands and should receive the most careful attention 
from the engineer, for the reason that there is where 
the greatest friction occurs, and if neglected for even 
a short time, trouble will occur. 

The main bearings of most engines are fitted with 
apparatus for oiling them by which the oil is dropped 
upon the top of the journal, when in fact the place that 
the oil is most needed is at the bottom or underside of 
the bearing. In horizontal engines, especially, there is 
a constant pressure on the bottom of the bearing, due 
to the weight of the flywheel and main shaft, and this 
pressure prevents the greater part of the oil, if fed in 
on top, from reaching the lower surface. Therefore 
the lubrication of pillow blocks may be greatly facil- 
itated by connecting, whenever it is possible to do so, 
at least one oil pipe in such a way that it will conduct 
the oil to the bottom of the bearing. In case a pillow 
block or other bearing shows signs of warming up, 
good results may often be obtained by using from 25 
to 50 per cent, of cylinder oil mixed with the regular 
engine oil. 

Every engineer should establish a regular system of 
oiling his engine, as for instance, by having regular 
intervals of time for going around the engine and 
inspecting all the working parts. A good rule is to 
make the rounds about every twenty minutes. In this 
way no part will be neglected, and the danger of 
having hot bearings or of other accidents happening 
will be greatly lessened. 

Many automatic cut off engines, especially those of 



ENGINE OPERATION 281 

the high speed type, are fitted with isochronal or shaft 
governors. There are various styles of these gov- 
ernors, but all or nearly all of them control the admis- 
sion of steam to the cylinder, and consequently the 
point of cut off by varying the angular advance of the 
eccentric, which in such engines is free to move across 
the shaft, being entirely under the control of the 
governor. 

Very close regulation is generally obtained by the 




ISOCHRONAL OR SHAFT GOVERNOR, BUCKEYE ENGINE CO. 

use of shaft governors, but particular attention should 
be given to the lubrication of the steam valve, which, 
with this class of engines, is generally a slide valve of 
some description, and although it may be ever so 
nicely balanced, yet if it does not get sufficient oil, the 
friction due to dry surfaces rubbing together, will put 
extra work on the governor, and the speed is liable to 
be irregular. 

Keying Up. To keep the working parts of an engine 
properly keyed up so as to take up the lost motion 



282 ENGINEERING 

without causing the bearings -to heat, is one of the 
most delicate and exacting duties of the engineer. 
Every engineer worthy of the name should aim to have 
a smooth and quietly running engine. In fact, this 
is one of the principal tests of his skill as an engineer. 

A few general suggestions may be given here, but 
much more depends upon the good judgment of the 
engineer himself. 

In connecting up an engine, as for instance, the 
crank pin and crosshead, the key should first be driven 
in until it is solid, that is, until the brasses clamp the 
pin tightly. Then place a small ruler across the face 
of the gib and key, and with the point of a knife blade, 
or a steel scriber, make a fine mark along the edge of 
the ruler. This will be the "solid mark.'' Now back 
the key up by light blows with the hammer, which 
should be of copper, until the brasses are just loose 
enough on the pin to permit a side movement of the 
rod. If the rod is very heavy, hold a block of wood 
against the side of the rod near the pin and give it a 
blow with a sledge. If there is no movement, back 
the key a little more, and keep trying until there is a 
side movement. There should be a space of at least 
3V in. between the sides of the brasses and the flange 
of the pin, so as to allow a slight side play. If it is 
found, after running a while, that there is too much 
lost motion, causing the engine to pound, put the ruler 
across the gib and key again, and with a lead pencil 
draw a line. Then loosen the set screw and drive the 
key in a distance equal to the width of the line, and 
no more. This process should be repeated at intervals 
until the pound is all gone, or the bearing begins to 
warm up slightly, indicating that the brasses are up as 
close as they will run. 



ENGINE OPERATION 283 

The adjustment of pillow blocks also requires a large 
measure of skill and good judgment, and should be 
done by degrees; but when once adjusted properly and 
kept well oiled, the matter of keeping them in good 
working condition becomes greatly simplified. 

If a pillow block, or other bearing filled with babbit 
metal, should become heated to such a temperature as 
to cause the metal to run, do hot shut down the engine 
at once and turn on a stream of cold water, because 
this will only make matters worse, causing the metal 
to stick to the journal, and the labor and trouble of 
cleaning it out will be increased. The best method to 
pursue in such an emergency is to gradually slow the 
engine down and keep it moving at as slow a speed as 
it will run, and in the meantime a small stream of 
cold water may be allowed to flow over the bearing, 
applying it to all parts as nearly as possible until it is 
cooled, after which the engine may be stopped and 
repairs made. 

Heating Feed Water. Every steam plant should be 
provided with one or more heaters for the purpose of 
utilizing the exhaust steam for heating the feed water, 
and the exhaust, not only of the engine, but of the 
feed pumps and all other steam pumps connected with 
the plant, should be led into it if possible. This 
applies especially to non-condensing engines, and 
even if the engine be a condensing engine the exhaust 
may be passed through a closed heater before going 
into the condenser. 

The percentage of saving in heat effected by heating 
the feed water with exhaust steam which would other- 
wise go to waste, may be ascertained by the following 
rule: 

Multiply the difference in the total heat in the 



284 ENGINEERING 

water above 32 , before and after heating, by 100, and 
divide the product by the total heat required to con- 
vert the water into steam from the initial temperature. 
The quotient will be the per cent, of saving. 

The following example will serve to illustrate the 
process: Suppose the initial temperature of the water 
to be 50 , and that by means of the heater its tem- 
perature is increased to 183 before entering the 
boiler. The steam pressure being 100 lbs. gauge, or 
115 lbs. absolute. By referring to Table 5, it will be 
seen that 

Water at 182. g° temp, contains 151. 5 heat units, 

« 5ao o << „ Ig • „ 

The difference = 133.5 neat units. 

One pound of steam at 115 lbs. absolute pressure 
contains above 32 , 1,185 neat units, and for each 
pound of water, at 50 , converted into steam at the 
above pressure, there would be required 1,185—18 = 
1 167 heat units; but 133.5 hear, units having been 
added to the water while passing through the heater, 
the problem now becomes — y^— =11.44 per cent., 
saving in heat. 

Two classes of heaters are available for this purpose, 
viz., open heaters and closed heaters. 

In the open heater the exhaust steam comes in con- 
tact with and mingles with the water, and a portion of 
it is condensed and returns to the boiler. In this 
respect the open heater has an advantage over the 
closed type, in which the water is kept separate from 
the exhaust steam by passing it through tubes that are 
surrounded by the steam which is confined in the outer 
shell of the heater. In some types of the closed heater 
the steam passes through the tubes, which are in turn 



ENGINE OPERATION 



285 



surrounded by the water. A heater of either class 
should be sufficiently large to allow the water to pass 
through it slowly, in order thai it may absorb all the 
heat possible. About one-third of a square foot of 
heating surface should be allowed per horse power for 
a closed heater, and it should have sufficient volume 
to contain water enough to supply the boilers for a 
quarter of an hour. If a heater is too small for the 
engine it is liable to cause ,„_. 

*=> STEAM 

back pressure on the ex- 
haust. 

There is no saving in 
heat, but rather a loss in 
using live steam to heat 
the feed water, but on the 
other hand, if the water is 
bad, it can be purified to a 
certain extent by passing 
it through a live steam 
heater on its way to the 
boiler. 

Probably the most eco- 
nomical device for feed- 
ing boilers is the exhaust 
injector, which not only 
feeds the boiler, but utilizes all the available heat in the 
exhaust steam and returns it to the boiler. The diffi- 
culties attending the use of the exhaust injector are 
that it cannot force water against a pressure above 75 
or 80 lbs., and that it will not lift its water supply by 
suction. 

The principle by which an injector is able to force 
water against a higher pressure than that of the steam 
by which it is operated, lies in the fact that the mix- 




SECTIONAL VIEW OF PEN- 
BERTHY INJECTOR. 



*!8b ENGINEERING 

ture of water and steam rushes with such velocity into 
the vacuum formed by the condensation of the steam, 
that the momentum thus acquired carries it into the 
boiler against the higher pressure. 

Live steam injectors, while being much less econom- 
ical than the steam pump with heater, are, neverthe- 
less, a valuable adjunct of a steam plant. They are 
lifting and non-lifting. A lifting injector in good con- 
dition, with no air leaks in the suction pipe, will raise 
the water by suction about 20 ft. With the non-lifting 
injector the water supply must flow into the injector, 
and it may be handled at a temperature as high as 
150 , although not so reliable as at lower temperatures. 

A good free working check valve and one that will 
not leak, is one of the most important requisites in the 
feeding of boilers, and especially is this the case when 
an injector is used. 

Sometimes an injector is prevented from working by 
dirt being drawn in through the suction pipe. This 
trouble can be avoided by fitting the pipe with a 
strainer. If the tubes become clogged with scale, they 
should be soaked in a dilute solution of muriatic acid, 
say one part of acid to ten parts of water. All the 
joints and connections should be air tight, and the 
valves should be properly packed, otherwise the 
injector will be a constant source of trouble. 

Changing the Speed of an Engine. It sometimes hap- 
pens that it is desired to permanently change the speed 
of an engine, and the method of doing this is as fol- 
lows: 

If it is desired to increase the speed but two or three 
revolutions, it can generally be accomplished by mov- 
ing the counter balance (which most governors have) 
farther out on the lever, although there is a limit to 



ENGINE OPERATION 287 

this, because if moved too far, either in, to decrease 
the speed, or out to increase the speed, the effect will be 
to destroy the true action of the governor, and its move- 
ments will be jerky. The location of the counter bal- 
ance should be at that point where the governor works 
the best at the speed at which it was designed to run, 
and which is generally marked on the governor. And 
this can only be determined by much patient experi- 
menting on the part of the engineer. If moving the 
counter balance does not bring about the desired 
increase of speed, the next move is to increase the 
diameter of the governor pulley so that the propor- 
tions of the pulleys on the engine shaft and the gov- 
ernor will be such that the governor will continue to 
run at its normal speed, while the speed of the engine 
has been increased the desired number of revolu- 
tions. 

To illustrate, assume the engine to be making 75 
revolutions per minute, and that the pulley on the 
engine shaft, upon which the governor belt runs, 
is 12 in. in diameter, and that the governor pulley is 8 
in. in diameter. 

Suppose it is desired to increase the speed of the 
engine to 85 revolutions per minute. First find the 
speed of the governor with the engine running at 75 
revolutions. 

The formula is, 
Speed of engine x diameter of shaft pulley , . 

Diameter of governor pulley ^ 

governor. Thus, <5 * 12 = 112. 5, revolutions for gov- 
ernor. 

Next find what the diameter of the governor pulley 
must be to allow the governor to still run at 112. 5 revo- 
lutions while the engine runs at 85 revolutions. 



288 ENGINEERING 

The formula is, 

Speed of engine x diameter of shaft pulley ,. 

^ i ^ — Qiameter 

Speed or governor 

of governor pulley. Thus, ^fip = 9.06 in., diameter 

of new pulley required for governor. 

Should it be desired to decrease the speed of the 

engine, the same rules and formula will apply for 

ascertaining the diameter of the governor pulley, which 

in this case would have to be reduced in size. 



Questions 

1. Into what two general classes may engines be 
divided? 

2. In what respect do they differ? 

3. What advantage has a compound engine over a 
simple engine? 

4. What advantage economically has a condensing 
engine over a non-condensing engine? 

5. How many kinds of condensers are there? 

6. Describe a jet condenser. 

7. Describe a surface condenser. 

8. Is an air pump absolutely necessary with all jet 
condensers? 

9. What is meant by an independent air pump and 
condenser? 

10. What three factors determine the quantity of 
condensing water required by an engine? 

11. What is the rule for ascertaining the quantity of 
condensing water required by an engine? 

12. How may the quantity of condensing water 
required per horse power per hour be ascertained? 

13. What precautions should be observed with a 
throttling governor? 



ENGINE OPERATION 289 

14. What general rules should be followed in the 
operation of an automatic cut off governor? 

15. What is the most reliable device for introducing 
oil into the valve chest and cylinder? 

16. How may the bottom guide of a horizontal 
engine be best lubricated? 

17. What reliable device may be used in the lubri- 
cation of the crank pin? 

18. What precautions should be observed in the 
lubrication of the main bearings or pillow blocks? 

19. What should be done with a pillow block that 
shows signs of warming up? 

20. How does an isochronal, or shaft governor, regu- 
late the speed of an engine? 

21. How is the shaft governor affected if the steam 
valve is not properly lubricated? 

22. Describe the proper method of keying up an 
engine. 

23. What should be done in case a main bearing 
becomes heated sufficiently to melt the babbitt? 

24. How may the exhaust be utilized to an advan- 
tage? 

25. What is the rule for ascertaining the percentage 
of saving in heat when an exhaust heater is used? 

26. What two classes of heaters are available? 

27. What is an open heater? 

28. Describe a closed heater. 

29. Is there a saving in heat effected by using alive 
steam heater? 

30. What advantage then is derived from its use? 

31. Upon what principle does an injector work? 

32. Into what two types are injectors divided? 

33. What particular valve in the feed pipe of a boiler 
should always be kept in good condition? 



290 ENGINEERING 

34. How may an injector that has become clogged 
with dirt or scale be cleaned? 

35. What precautions should be observed in fitting 
up an injector? 

^6. How may the speed of an engine be slightly 
increased? 

37. If it is desired to increase the speed consider- 
ably, how may it be done? 

38. If it is desired to decrease the speed, what 
changes are necessary? 



Engineering 

PART II 



INTRODUCTION TO PART II 

In Chapters I, II and III of Part I the construction, 
setting and operation of steam boilers is treated upon 
at some length, but as there is a constant demand in 
the manufacturing world for higher steam pressures, 
the author considers that it would no doubt be of great 
benefit to his readers if these topics were dealt with 
more in detail. This is done in Chapters I and II, and 
the subject of mechanical stokers and furnaces is 
taken up in Chapter III. 

Since the inauguration of the twentieth century there 
has been introduced to the engineering profession a 
comparatively new prime mover, in the shape of the 
steam turbine, and judging from present indications it 
has come to stay. Therefore it behooves engineers to 
make themselves acquainted with it, and the sooner 
they do so the more will they be benefited by the 
advent of this stranger. 

In the remaining portion of Part II the author has 
endeavored to lay before his readers a plain, practical 
description of each one of the four leading types of 
steam turbines that are being manufactured and used 
in this country at the present time. 

C. F. S. 

April, 1905. 



293 



Engineering 

PART II 

CHAPTER I 
THE BOILER 

Importance of correct knowledge of the construction and 
strength of steam boilers— Tensile strength of steel boiler 
plates — Dr. Thurston's specifications — Specifications of U. S. 
board of inspectors of steam vessels — Punched and drilled 
plates — Rivets and rivet iron and steel — Efficiency of the 
joints — Proportions of double riveted butt joints — Lloyd's 
rules for thickness of plate and diameter of rivets— Cor- 
rect design of triple riveted butt joints — Calculations for 
efficiency of different forms of joints — Discussion of various 
ways in which failure may occur in different styles of joints 
— Necessity for higher efficiencies in riveted joints — Quad- 
ruple and quintuple butt joints— Staying flat surfaces — 
Different methods of staying a boiler — Correctly designed 
stays — Stay bolts for fire box boilers — The Belpaire boiler — 
Vanderbilt Locomotive with Morison fire box — Gusset stays — 
Through stay rods — Calculating strength of stayed surfaces — 
Area of segments — Proper spacing of stays — Strength of un- 
stayed surfaces — Dished heads — Welded seams. 

As it is of the highest importance, not only to the 
engineer in charge of the plant, but also to his assist- 
ants, and in fact to all persons whose business com- 
pels them to be in the vicinity of the boiler-room, that 
there should be absolutely no doubt as to the safe 
construction of the boilers and their ability to with- 
stand the pressures under which they are operated, the 
295 



Z\)b ENGINEERING 

author has compiled the following additional data 
regarding the construction and strength of boilers. 
The deductions and reports of tests and experiments 
made by such eminent authorities as Dr. Thurston, 
Prof. Wm. Kent, Dr. Peabody, D. K. Clark, Hutton 
and many other experts have been consulted, and the 
author has also added the results of his own obser- 
vations, collected during an experience of thirty-five 
years as a practical engineer. 

When steel was first introduced as a material for 
boiler plate, it was customary to demand a high tensile 
strength, 70,000 to 74,000 lbs. persq. in., but experience 
and practice demonstrated in course of time that it 
was much safer to use a material of lower tensile 
strength. It was found that with steel boiler plate of 
high tenacity there was great liability of its cracking, 
and also of certain changes occurring in its physical 
properties, brought about by the variations in tem- 
perature to which it was exposed. Consequently 
present-day specifications for steel boiler plate call for 
tensile strengths running from 55,000 to 66,000 lbs., 
usually 60,000 lbs. per sq. in. Dr. Thurston gives 
what he calls "good specifications" for boiler steel as 
follows: "Sheets to be of uniform thickness, smooth 
finish, and sheared closely to size ordered. Tensile 
strength to be 60,000 lbs. per sq. in. for fire box sheets 
and 55,000 lbs. per sq. in. for shell sheets. Work- 
ing test: a piece from each sheet to be heated to a 
dark cherry red, plunged into water at 6o° and bent 
double, cold, under the hammer. Such piece to show 
no flaw after bending. The U. S. Board of Supervising 
Inspectors of Steam Vessels prescribes, in Section 3 of 
General Rules and Regulations, the following method 
for ascertaining the tensile strength of steel plate for 



THE BOILER 297 

boilers: "There shall be taken from each sheet to be 
used in shell or other parts of boiler which are sub- 
ject to tensile strain, a test piece prepared in form 
according to the following diagram: 



-jdSn&L. n &. Jkr<sJ/e/ Section 
T , ¥~ f M>t/e r ssTM,n9 r ' 

! C - ! tjk 



Aboi/J-Z 
— * 



A J .:.{:.^:..Mo U fys~. 



TEST PIECE. 



The straight part in center shall be 9 in. in length 
and 1 in. in width, marked with light prick punch 
marks at distances 1 in. apart, as shown, spaced so as 
to give 8 in. in length. The sample must show, when 
tested, an elongation of at least 25 per cent in a length 
of 2 in. for thickness up to % in. inclusive; in a length 
of 4 in., for over % in. to T \ in. inclusive; in a length 
of 6 in., for all plates over T \ in. and under 1% in. in 
thickness. The samples shall also be capable of being 
bent to a curve of which the inner radius is not greater 
than i T /i times the thickness of the plates, after having 
been heated uniformly to a low cherry red and 
quenched in water of 82 ° F." 

Punched and Drilled Plates. Much has been written 
on this subject, and it is still open for discussion. If 
the material is a good, soft steel, punched sheets are 
apparently as strong and in some instances stronger 
than drilled, especially is this the case with regard to 
the shearing resistance of the rivets, which is greater 
with punched than with drilled holes. 

Concerning rivets and riv.et iron and steel Dr. 



298 



ENGINEERING 



Thurston has this to say in his "Manual of Steam 
Boilers": "Rivet iron should have a tenacity in the 
bar approaching 60,000 lbs. per sq. in., and should be 
as ductile as the very best boiler plate when cold. A 
good ^-in. iron rivet can be doubled up and hammered 
together cold without exhibiting a trace of fracture." 
The shearing resistance of iron rivets is about 85 per 
cent and that of steel rivets about 77 per cent of the 
tenacity of the original bar, as shown by experiments 
made by Greig and Eyth. The researches made by 
Wohler demonstrated that the shearing strength of 
iron was about four-fifths of the tensile strength. 

The tables that follow have been compiled from the 
highest authorities and show the results of a long and 
exhaustive series of tests and experiments made in 
order to ascertain the proportions of riveted joints that 
will give the highest efficiencies. 

The following Table 11 gives the diameters of rivets 
for various thicknesses of plates and is calculated 
according to a rule given by Unwin. 

TABLE 11 

Table of Diameters of Rivets* 



Thickness of 
Plate 


Diameter of Rivet 


Thickness of Plate 


Diameter of Rivet 


V4 inch 

5 /l6 " 

3 / 8 " 
7 / 16 " 
V 2 " 


V 2 inch 

9 /l6 " 
U /l6 " 

3 / 4 " 
13 /l6 " 


9 /ie inch 
5 /s " 
3 / 4 " 
Vs " 

1 


V 8 inch 

15 /l6 " 
lVl6 " 
IVs " 

1V4 " 



The efficiency of the joint is the percentage of the 
strength of the solid plate that is retained in the joint, 



* Machine design— W. C. Unwin. 



THE BOILER 



299 



and it depends upon the kind of joint and method of 
construction. 

If the thickness of the plate is more than y 2 in., the 
joint should always be of the double butt type. 

The diameters of rivets, rivet holes, pitch and 
efficiency of joint, as given in the following Table 12, 
which was published in the "Locomotive" several 
years ago, were adopted at the time by some of the 
best establishments in the United States.* 

TABLE 12 

Proportions and Efficiencies of Riveted Joints 



Inch 


Inch 


74 


5 U 


b /« 


"/ifi 


n U 


3 /4 


2 


2Vi« 


3 


3Vs 


.66 


.64 


.77 


.76 



Inch Inch 



Thickness of plate 

Diameter of rivet 

Diameter of rivet-hole 

Pitch for single riveting 

Pitch for double riveting 

Efficiency — single-riveted joint 
Efficiency — double-riveted joint 



3 /s 
3 / 4 

13 /l6 

2Vs 
3V 4 
.62 
.75 



Vl6 
13 /l6 

Vs 
2 3 /ie 
3 3 / 8 
.60 
.74 



v 2 

15 /l6 

2V 4 

3V 2 
.58 
.73 



Concerning the proportions of double-riveted 
butt joints, Prof. Kent says: "Practically it may 
be said that we get a double-riveted butt joint 
of maximum strength by making the diameter of 
the rivet about 1.8 times the thickness of the plate, 
and making the pitch 4.1 times the diameter of the 
hole." 

Table 13 as given below is condensed from the report 
of a test of double-riveted lap and butt joints. f In 



* Thurston's "Manual of Steam Boilers.' 
tProc. Inst. M. E., Oct., 1888. 



300 



ENGINEERING 



this test the tensile strength of the plates was 56,000 to 
58,000 lbs. per sq. in., and the shearing resistance of 
the rivets (steel) was about 50,000 lbs. per sq. in. 



TABLE 13 

Diameter and Pitch of Rivets — Double-riveted Joint 



Kind of Joint 


Thickness of 
Plate 


Diameter of 
Rivet 


Ratio of Pitch to 
Diameter 


Lap 
Butt 
Butt 
Butt 


| inch 

1 " 
3 " 

1 " 


0.8 inches 
0.7 " 
1.1 " 
1.3 " 


3 . 6 inches 
3.9 " 
4.0 " 
3.9 " 



Lloyd's rules, condensed, are as follows: 
Lloyd's Rules — Thickness of Plate and Diameter of Rivets 



Thickness of 


Diameter of 


Thickness of 


Diameter of 


Plate 


Rivets 


Plate 


Rivets 


3 /s inch 


5 / 8 inch 


3 / 4 " 


7 Is inch 


Vie " 


5 / 8 " 


13 /l6 " 


Vs " 


V2 " 


3 / 4 " 


Vs " 


1 


9 /l6 " 


3 / 4 " 


15 /l6 " 


1 


5 /8 " 


3 / 4 " 


1 


1 


n /l6 " 


Vs " 







The following Table 14 is condensed from one calcu- 
lated by Prof. Kent,* in which he assumes the shearing 
strength of the rivets to be four-fifths of the tensile 
strength of the plate per square inch, and the 
excess strength of the perforated plate to be 10 per 
cent. 



* Kent's "Mechanical Engineer's Pocket-Book," page 362. 



THE BOILER 



301 



TABLE 14 







Pitch 


Efficiency 


Thickness 
of Plate 


Diameter 
of Hole 








Single 1 


Double 


Single 


Double 






Riveting 


Riveting 


Riveting 


Riveting 


Inches 


Inches 


Inches 


Inches 


Per Cent 


Per Cent 


3 /s 


Vs 


2.04 


3.20 


57.1 


72:7 


Vie 


1 


2.30 


3.61 


56.6 


72.3 


Va 


1 


2.14 


3.28 


53.3 


70.0 


V2 


IVs 


2.57 


4.01 


56.2 


72.0 


7l6 


1 


2.01 


3.03 


50.4 


67.0 


9 /l6 


IVs 


2.41 


3.69 


53.3 


69.5 


9 /l6 


1V4 


2.83 


4.42 


55.9 


71.5 


Vs 


- 1 


1.91 


2.82 


47.7 


64 6 


Vs 


IVs 


2.28 


3.43 


50.7 


67.3 


5 / 8 


1V4 


2.67 


4.10 


53.3 


69.5 



Another table of joint efficiencies as given by Dr. 
Thurston* is as follows, slightly condensed from the 
original calculation: 



Vt fi " 


V*' ' 


5 /s' 


3 / 4 ' 


Vs' 


1' 


.53 


.52 


.48 


.47 


.45 


.43 



TABLE 15 

Single riveting 

Plate thickness. 5 / 16 ' ' 3 /s' 

Efficiency 55 .55 

Double riveting 

Plate thickness. 3 /s" 7 / 16 " V2" 3 U" V 1" 
Efficiency 73 .72 .71 .66 .64 .63 

The author has been at considerable pains to compile 
Tables 16, 17 and 18, giving proportions and efficiencies 
of single lap, double lap and butt, and triple-riveted 
butt joints. The highest authorities have been con- 
sulted in the computation of these tables and great 
care exercised in the calculations. 



* Thurston's "Manual of Steam Boilers," page 119. 



302 



ENGINEERING 



TABLE 16 

Proportions of Single-riveted Lap Joints 



Thickness of Plate 


Diameter of Rivet 


Pitch of Rivet 


Efficiency 


Inches 


Inches 


Inches 


Per Cent 


716 


9 /l6 


1.13 


50.5 




5 /s 


1.33 


53.3 


" 


n /l6 


1.55 


55.7 


3 /s 


3 / 4 


1.60 


53.3 




7 /s 


2.04 


57.1 


7 /l6 


7 /s 


1.87 


53.2 




1 


2.30 


56.6 


^k 


1 


2.14 


53.3 




IVs 


2.57 


56.2 


9 /l6 


1 


2.01 


50.4 




IVs 


2.41 


53.3 


" 


1V4 


2.83 


55.9 


5 /s 


IVs 


2.28 


50.7 




1V4 


2.67 


53.3 



It will be noticed that in single-riveted lap joints the 
highest efficiencies are attained when the diameter of 
the rivet hole is about 2^3 times the thickness of the 
plate, and the pitch of the rivet 2^ times the diameter 
of the hole. 

With the double-riveted joint it appears, according 
to Table 17, that in order to obtain the highest 
efficiency the joint should be designed so that the 
diameter of the rivet hole will be from if to 2 times 
the thickness of plate, and the pitch should be from 
3,M3 to 3^ times the diameter of the hole. Concerning 
the thickness of plates Dr. Thurston has this to say:* 
"Very thin plates cannot be well caulked, and thick 
plates cannot be safely riveted. The limits are about 
% of an inch for the lower limit, and % of an inch for 
the higher limit." The riveting machine, however, 
overcomes the difficulty with very thick plates. 

■■* Thurston's "Manual of Steam Boilers," page 120. 



THE BOILER 303 

TABLE 17 
Proportions of Double-riveted Lap and Butt Joints 



Thickness of 


Diameter of 






Plate 


Rivet 


Pitch of Rivet 


Efficiency 


5 /ie inch 


9 /ie inch 


1 .71 inches 


67 . 1 per cent 


5 /l6 " 


5 / 8 " 


2.05 " 


69.5 ' 




3 / 8 " 


3 / 4 " 


2.46 " 


69.5 ' 




3 / 8 " 


7 U " 


3.20 " 


72.7 ' 




7 /l6 " 


3 U " 


2.21 " 


66.2 ' 




Vl6 " 


Vs " 


2 86 " 


69.4 




Vl6 " 


1 


3 61 " 


72.3 « 




Vi " 


1 


3.28 " 


70.0 ' 




Vi " 


IVs " 


4.01 " 


72.0 ' 




9 /l6 " 


1 


3.03 " 


67.0 ' 




9 /l6 " 


IVs " 


3.69 " 


69.5 ' 




9 /l6 " 


1V4 " 


4.42 " 


71.5 ' 




5 /s " 


IVs' " 


3.43 " 


67.3 ' 




5 / 8 " 


1V4 " 


4.10 " 


69.5 ' 




3 / 4 " 


1 


2.50 " 


72.0 ' 




7 / 8 " 


IVs " 


3.94 " 


74.2 ' 




1 


1V4 " 


4.10 " 


76.1 ' 





The triple-riveted butt joint with two welts, one in- 
side and one outside, has two rows of rivets in double 
shear and one outer row in single shear on each side 
of the butt, the pitch of rivets in the outer rows being 
twice the pitch of the inner rows. One of the welts is 
wide enough for the three rows of rivets each side of 
the butt, while the other welt takes in only the two 
close pitch rows. 

When properly designed, this form of joint has a 
high efficiency, and is to be relied upon. Table 18 
gives proportions and efficiencies, and it will be noted 
that the highest degree of efficiency is shown when the 
diameter of rivet hole is from ij£ to 1% times the 
thickness of plate, and the pitch of the rivets is from 
lY 2 to 4 times the diameter of the hole. This, of 



304 



ENGINEERING 



course, refers to the pitch of the close rows of rivets, 
and not the two outer rows. 



TABLE 18 

Proportions of Triple-riveted Butt Joints with Inside and 
Outside Welt 



Thickness of 


Diameter of 


Pitch of 


Pitch of 


Efficiency 
Per Cent 


Plate 


Rivet 


Rivet 


Outer Rows 


Inches 


Inches 


Inches 


Inches 


7s 


u /ie 


3.25 


6.5 


84 


Vic 


M /ie 


3.25 


6.5 


85 


72 


U /lG 


3.25 


6.5 


83 


7io 


Vs 


3.50 


7.0 


84 


7s 


1 


3.50 


7.0 


86 


74 


lVl6 


3.50 


7.0 


85 


Vs 


IVs 


3.75 


7.5 


86 


l 


1V4 


3.87 


7.7 


84 



Some simple rules are given in Chapter I, Part I, for 
finding the percentage of efficiency, or in other words 
the ratio of the strength of the riveted joint to the 
strength of the solid plate. In those calculations the 
tensile strength of the rivets was assumed to be 38,000 
to 40,000 lbs. per sq. in. The highest efficiency is 
attained in a riveted joint when the tensile strength of 
the rods from which the rivets are cut approaches that 
of the plates, and when the proportions of the joint 
are such that the tensile strength of the plates, the 
shearing strength of the rivets, and the crushing 
resistance of the rivets and plate, for a given section 
or unit strip, are as nearly equal as it is possible to 
secure them. 

A few examples of calculations for efficiency will be 
given, taking the three forms of riveted joints in most 
common use. The following notation will be used 
throughout: 



THE BOILER 



305 



T.S. = Tensile strength of plate per square inch. 
T = Thickness of plate. 

C = Crushing resistance of plate and rivets. 
A = Sectional area of rivets. 
S = Shearing strength of rivets. 
D = Diameter of hole (also diameter of rivets 

when driven). 
P = Pitch of rivets. 
In the calculations that follow T.S. will be assumed 
to be 6o,000 lbs., S will be taken at 45,000 lbs., and the 
value of C may be assumed to be 90,000 to 95,000. 

Fig. 97 shows a double-riveted lap joint. The style 
of riveting in this joint 
is what is known as 
chain riveting. 

In case the rivets are 
staggered, the same 
rules for calculating 
the efficiency will hold 
as with chain riveting, 
for the reason that 
with either style of 
riveting the unit strip 
of plate has a width equal to the pitch or distance p, 
Fig. 97. ^ 

The dimensions of the joint under consideration are 
as follows: P = 3^ in., T = T 7 6 - in., D = I in. (which is 
also diameter of driven rivet). 

The strength of the unit strip of solid plate is 
PxTxT.S. =85,312. 

The strength of net section of plate after drilling is 
P - D x T x T.S. = 59,062. 

The shearing resistance of two rivets is 2A x S = 70, 
686. 




FIGURE 97. 



.306 



ENGINEERING 



The crushing resistance of rivets and plate is 
Dx2xTxC = 78,750. 

It thus appears that the weakest part of the joint is 
the net strip or section of plate, the strength of which 
is 59,062 and the efficiency = 59,062 x 100 -*- 85,312 = 
69.2 per cent. 

A double-riveted butt joint is illustrated by Fig. 
98, and the dimensions are as follows: 

P, inner row 
of rivets = 2^ 
in. 

P', outer row 
of rivets = 5^ 
in. 

Tof plate and 
butt straps = T \ 
in. 

Dof hole and 
driven rivet = 1 
in. 

Failure may 

occur in this joint in five distinct ways, which will be 
taken up in their order. 

1. Tearing of the plate at the outer row of rivets. 
The net strength at this point is P-DxTxT.S., 
which, expressed in plain figures, results as follows: 
5.5- 1 x .4375 x 60,000= 118,125. 

2. Shearing two rivets in double shear and one in . 
single shear. Should this occur, the two rivets in the 
inner row would be sheared on both sides of the plate, 
thus being in double shear. Opposed to this strain 
there are four sections of rivets, two for each rivet. 
Then at the outer row of rivets in the unit strip there 
is the area of one rivet in single shear to be added, 




FIGURE 98. 



THE BOILER 



307 



The total resistance, therefore, is 5A x S as follows: 
.7854 x 5 x 45,000 = 176,715. 

3. The plate may tear at the inner row of rivets and 
shear one rivet in the outer row. The resistance in 
this case would be P' — 2D x T x T.S. + A x S as 
follows: 5.5 -2 x .4375 x 60,000 + .7854 x 45,000 = 
127,218. 

4. Failure may occur by crushing in front of three 
rivets. Opposed to this is 3D xTxC, or 1 x 3 x -4375 x 
95,000= 124,687. 

5. Failure may occur by crushing in front of two 
rivets and shearing one. The resistance is represented 
by 2D x T x C + iA x S; expressed in figures, Ix2x 
•4375 x 95.000 + .7854 x 45,000 = 1 18,468. 

The strength of a solid strip of plate 5^ in. wide 
before drilling is P' x T x T.S. , or 5. 5 x .4375 x 60,000 = 
144,375, an d tne efficiency of the joint is 1 18,125 x 100 ■*■ 
144,375 = 81. 1 per cent. 

A triple-riveted butt joint is shown in Fig. 99, the 
dimensions of 
which are as fol- 
lows: 

T~*.in. 

D = |f in. 

A = .69 in. 

P =3 3 /s in. 

P' = 6^ in. 

Failure may 
occur in this 
joint in either 
one of five 
ways. 

I. By tearing the plate at the outer row of rivets 
where the pitch is 6% in. The net strength of the unit 




FIGURE 99. 



308 ENGINEERING 

strip at this point isP'-DxTx T.S., found as follows: 
675 - -9375 x -4375 x 60,000 = 152,578. 

2. By shearing four rivets in double shear and one 
in single shear. In this instance, of the four rivets in 
double shear, each one presents two sections, and 
the one in single shear presents one, fc thus making 
a total of nine sections of rivets to be sheared, 
and the strength is 9A x S, or .69 x 9 x 45,000 = 
279,450. 

3. Rupture of the plate at the middle row of rivets 
and shearing one rivet. Opposed to this strain the 
strength is P' - 2D x T x T.S. t iA x S, equivalent to 
6-75 - (-9375 x 2) x .4375 x 60,000 + .69 x 90,000 = 
190,068. 

4. Crushing in front of four rivets and shearing one 
rivet. The resistance in this instance is 4D x T x C + 
1 A x S, or .9375 x 4 x .4375 x 90,000 + .69 x 45,000 = 
178,706. 

5. Failure may be caused by crushing in front of 
five rivets, four of which pass through both the 
inside and outside butt straps, while the fifth rivet 
passes through the inside strap only, and the resist- 
ance is 5D x T x C, equivalent to .9375 x 5 x 90,000 = 
184,570. 

The strength of the unit strip of plate before drilling 
isP'xTx T.S., or 6.75 x .4375 x 60,000 = 177,187, and 
the efficiency is 152,578x100-177,187 = 86 per 
cent. 

With the constantly increasing demand for higher 
steam pressures, the necessity for higher efficiencies in 
the riveted joints of boilers becomes more apparent, 
and of late years quadruple and even quintuple-riveted 
butt joints have in many instances come into use. The 
quadruple butt joint when properly designed shows a 



THE BOILER 



309 



high efficiency, in some cases as high as 94.6 per cent. 
Fig. 100 illustrates a joint of this kind, and the 
dimensions are as follows: 

T=y 2 in. 

D = i| in. 

A = .69 in. 

P, inner rows = 3^ in. 

?', 1st outer row = jy 2 in. 

P", 2d outer row = 15 in. 

The two inner rows of rivets extend through the 




FIGURE 100. 



main plate and both the inside and outside cover 
plates or butt straps. 

The two outer rows reach through the main plate 
and inside cover plate only, the first outer row having 
twice the pitch of the inner rows, and the second 
outer row has twice the pitch of the first. 



310 ENGINEERING 

Taking a strip or section of plate 15 in. wide (pitch 
of outer row), there are four ways in which this joint 
may fail. 

1. By tearing of the plate at the outer row of rivets. 
The resistance is P" — DxTxT.S., or 15 — .9375 x 
.5 x 60,000 = 421,875. 

2. By shearing eight rivets in double shear and three 
in single shear. The strength in resistance is 19A x S, 
or .69 x 19 x 45,000 = 589,950. 

3. By tearing at inner rows of rivets and shearing 
three rivets. The resistance is P" - 4D x T x T.S. + 
3A x S, or 15 -(.9375 x 4) x .5 x 60,000+ .69 x 3 x45,000 = 
430,650. 

4. By tearing at the first outer row of rivets, where 
the pitch is 7^ in., and shearing one rivet. The 
resistance is P" — 2D x T x T.S. + A x S, or 15 — (.9375 x 
2) x .5 x 60,000+ .69 x 45,000 = 424,800. 

It appears that the weakest part of the joint is at the 
outer row of rivets, where the net strength is 421,875. 
The strength of the solid strip of plate 15 in. wide 
before drilling is P" x T x T.S., or 15 x .5 x 60,000 = 
450,000, and the efficiency is 421,875 x 100 ■*■ 450,000 = 
93.7 per cent. 

Staying Flat Surfaces. The proper staying or bracing 
of all flat surfaces in steam boilers is a highly important 
problem, and while there are various methods of 
bracing resorted to, still, as Dr. Peabody says, "the 
staying of a flat surface consists essentially in holding 
it against pressure at a series of isolated points which 
are arranged in regular or symmetrical pattern." The 
cylindrical shell of a boiler does not need bracing for 
the very simple reason that the internal pressure tends 
to keep it cylindrical. On the contrary the internal 
pressure has a constant tendency to bulge out the flat 



THE BOILER 



311 




FIGURE 101. 



surface. Rule 2, Section 6, of the rules of the U. S. 
Supervising Inspectors provides as follows: "No braces 
or stays hereafter to be employed in the construction 
of boilers shall be 
allowed a greater 
strain than 6,000 lbs. 
per sq. in. of sec- 
tion." 

The method to be 
employed in staying 
a boiler depends upon the type of boiler and the pressure 
to be carried. Formerly when comparatively low pres- 
sures were used (60 to 75 lbs. per sq. in.) the diagonal 
crow foot brace was considered amply sufficient for stay- 
ing the flat heads of boilers of the cylindrical tubular 
type, both above and below the tubes, but in the present 
age, when much higher pressures are demanded, 
through stay rods are largely employed. These are 
soft steel or iron rods i}( to 2 in. in diameter, extend- 
ing through from head to head, with a pull at right 
angles to the plate, thus having a great advantage 
over the diagonal stay in that the pull on the diagonal 

tay per square inch of 
section is more than 5 
per cent in excess of 
what a through stay 
would have to resist 
under the same condi- 
tions of pressure, etc. 
The method of calculation for diagonal bracing is 
given in Chapter I and will not be discussed here. 

The weakest portion of the crow foot brace when in 
position is at the foot end, where it is connected to the 
head by two rivets. With a correctly designed brace 




figure 102. 



312 



ENGINEERING 




FIGURE 103. 



the pull on these rivets is direct and the tensile strength 
of the material needs to be considered only, but if the 
form of the brace is such as to bring the rivet holes 
above or below the center line of the 
brace, or if the rivets are pitched too 
far from the body of the brace, there 
will be a certain leverage exerted upon 
the rivets in addition to the direct pull. 
Fig. 101 shows a brace of incorrect 
design and Figs. 102 and 103 show 
braces designed along correct lines. 

Other methods of staying, besides 
the crow foot brace and through stays, 
consist of gusset stays, and for locomo- 
tives and other fire box boilers screwed 
stay bolts are employed to tie the fire 
box to the external shell. The. holes for these stay 
bolts are punched or drilled before the fire box is put 
in place. After it is in and riveted along the lower 
edge to the foundation ring, or mud ring as it is some- 
times called, a continuous thread is tapped in the 
holes in both the outside plate and the fire sheet 
by running a long tap through both plates. The 
steel stay bolt is then screwed through the plates 
and allowed to project enough at each end to permit 
of its being riveted cold. Stay bolts are liable 
to be broken by the unequal expansion of the fire 
box and outer shell, and a small hole should be 
drilled in the center of the bolt, from the outer end 
nearly through to the inner end. Then in case a bolt 
breaks, steam or water will blow out through the small 
hole, and the break will be discovered at once. The 
problem of properly staying the flat crown sheet of a 
horizontal fire box boiler, especially a locomotive 



THE BOILER 313 

boiler, is a very difficult one and has taxed the inven- 
tive genius of some of the most eminent engineers. 

Before the invention of the Belpaire boiler, with its 
outside or shell plate flat above the fire box, the only 
method of staying the crown sheet was by the use of 
cumbersome crown bars or double girders extending 
across the top of the crown sheet and supported at the 
ends by special castings that rest on the edges of the 
side sheets and on the flange of the crown sheet. At 
intervals of 4 or 5 in. crown bolts are placed, having 
the head inside the fire box and the nut bearing on a 
plate on top of the girder. There is also a thimble for 
each bolt to pass through, between the top of the 
crown sheet and the girder. These thimbles maintain 
the proper distance between the crown sheet and 
girder and allow the water to circulate freely. 

The Belpaire fire box dispenses with girders and 
permits the use of through stays from the top of the 
fiat outside plate through the crown sheet and secured 
at each end by nuts and copper washers. 

For simplicity of construction and great strength the 
cylindrical form of fire box known as the Morison 
corrugated furnace has proved to be very successful. 
This form of fire box was in 1899 applied to a loco- 
motive by Mr. Cornelius Vanderbilt, at the time assist- 
ant superintendent of motive power of the New York 
Central and Hudson River R. R. This furnace was 
rolled of fy-'m. steel, is 59 in. internal diameter and 11 
ft. 2% in. in length. It was tested under an external 
pressure of 500 lbs. per sq. in. before being placed in 
the boiler. It is carried at the front end by a row of 
radial sling stays from the outside plate, and supported 
at the rear by the back head. Figs. 104 and 105 show 
respectively a sectional view and an end elevation of 



314 



ENGINEERING 




this boiler. It will 
be seen at once 
that the question 
of stays for a fire 
box of this type 
becomes very sim- 
ple. The boiler 
has proved to be 
so satisfactory that 
the company has 
since had five more 
of the same type 
constructed. 

Gusset stays are 
used mainly in 
boilers of the Lan- 
cashire model and 
are triangular- 
shaped plates 
sheared to the 
proper form and 
having- two angle 
irons riveted to the 
edges that come 
against the shell 
and the head. The 
angle irons are 
then riveted to the 
shell and the flat 
head. This form 
of brace is simple 
and solid, but its 
chief defect is, 
that it is very rigid 



THE BOILER 



1515 



and does not allow for the unequal expansion of the in- 
ternal furnace flues and the shell. Fig. 106 illustrates a 
gusset stay and the method of applying it. 

Coming now to through stay rods, it is safe to say 
that whenever and wherever it is possible to apply 
them they should be used. In all cases they should 




Vertical Section A-B. 

nog 




End Elevation, 
Sfiowing Attachment of Long. Stays. 



fc— fl^'-H Half End Elevation 
Half Section C-D. j of Smoke-Box. 



FIGURE 105. 

be placed far enough apart to allow a man to pass 
between them for the purposes of inspection and wash- 
ing out of the boiler. Through stay rods are usually 
spaced 14 in. apart horizontally and about the same 
distance vertically. The ends, as far back as the 
threads run, are swaged larger than the body, so that 
the diameter at the bottom of the thread is greater 
than the diameter of the body. There are several 



316 



ENGINEERING 



methods of applying through stays. One of the most 
common, especially for land boilers, is to allow the 
ends of the rod • to project through the plates to be 
stayed, and holding them in place by a nut and copper 
washer, both inside and outside the plate. Another 
and still better plan is to rivet 6-in. channel bars across 

the head, inside above 
' the tubes, the number 
of bars depending 
upon the height of the 
segment to be stayed. 
The channel bars 
are drilled to corre- 
spond with the holes 
that are drilled in the 
plate to receive the stay rods, which latter are then 
secured by inside and outside nuts and copper washers. 



jTTSW' T 


10 x 


i° / u 





FIGURE 106. 




FIGURE 107. 



These channel bars act as girders and serve to greatly 
strengthen the head or flat plate. Fig. 107 will serve 
to illustrate this method. 



THE BOILER 



317 



Sometimes a combination of channel bar and 
diagonal crow foot braces is used, as shown by Fig. 108. 

A good form of diagonal crow foot stay is obtained 
by using dou- 
ble crow feet, 
made of pieces 
of boiler plate 
bent as shown 
by Fig. 109 
and riveted to 
the plate by 
four rivets. A 
hole is drilled 
through the 
body of the 
crow foot, and 
a bolt pass- 
ing through 
this secures th 




0000( t 

FIGURE 108. 



forked end of the stay. 

Another method of securing through stays to the 

heads is shown by Fig. no and is applied where too 

many stay rods would be required 

to connect all the points to be 

stayed. A tee iron is first riveted 

to the flat plate to be stayed, and 

two V-shaped forgings are bolted 

to it as shown. The through stay 

is then bolted to the forgings, and 

thus two points in the flat head 

are supported by one stay. It will 

readily be seen that this method will reduce the number 

of through stay rods required. 

Calculating the Strength of Stayed Surfaces. In cal- 
culations for ascertaining the strength of stayed sur- 




figuke 109. 



318 



ENGINEERING 



faces, or for finding the number of stays required for 
any given flat surface in a boiler, the working pressure 
being known, it must be remembered that each stay 
is subjected to the pressure on an area bounded by 
lines drawn midway between it and its neighbors. 
Therefore the area in square inches, of the surface to 




FIGURE 110. 



be supported by each stay, equals the square of the 
pitch or distance in inches between centers of the 
points of connection of the stays to the flat plate. 
Thus, suppose the stays in a certain boiler are spaced 
8 in. apart, the area sustained by each stay = 8x8 = 
64 sq. in., or assume the stay bolts in a locomotive fire 
box to be pitched 4^ in. each way, the area sup- 
ported by each stay bolt = 4^2 x 4>2 = 20*4 sq. in. 
Again taking through stay rods, suppose, for example, 



THE BOILER 319 

the through stays shown in Fig. 107 to be spaced 15 
in. horizontally and 14 in. vertically, the area sup- 
ported by each stay = 15 x 14 = 210 sq. in. 

The minimum factor of safety for stays, stay bolts 
and braces is 8, and this factor should enter into all 
computations of the strength of stayed surfaces. 

The pitch for stays depends upon the thickness of 
the plate to be supported, and the maximum pressure 
to be carried. 

In computing the total area of the stayed surface it 
is safe to assume that the flange of the plate, where it 
is riveted to the shell, sufficiently strengthens the plate 
for a distance of 2 in. from the shell, also that the 
tubes act as stays for a space of 2 in. above the top 
row. Therefore the area of that portion of the flat 
head or plate bounded by an imaginary line drawn at 
a distance of 2 in. from the shell and the same dis- 
tance from the last row of tubes is the area to be 
stayed. This surface may be in the form of a segment 
of a circle, as with a horizontal cylindrical boiler, or 
it may be rectangular in shape, as in the case of a 
locomotive or other fire box boiler. Other forms of 
stayed surfaces are often encountered, but in general 
the rules applicable to segments or rectangular figures 
will suffice for ascertaining the areas. 

The method, of finding the area of the segmental 
portion of the head above the tubes is given in Chapter 
I, pages 22 and 23, and will not be enlarged upon here, 
except to add Table 19, which covers a much greater 
number of segments than Table 1, page 22, does. The 
diameter of the circle and the rise or height of the 
segment being known, the area of the segment may 
be found by the following rule: 

Rule. Divide the height of the segment by the 



320 



ENGINEERING 



TABLE 19 

Areas of Segments of a Circle 



Ratio 


Area 


Ratio 


Area 


Ratio 


Area 


Ratio 


Area 


.2 


11182 


.243 


14751 


.286 


18542 


.329 


. 22509 


'201 


11262 


.244 


14837 


.287 


18633 


.33 


. 22603 


.202 


11343 


.245 


14923 


.288 


18723 


.331 


. 22697 


.203 


11423 


.246 


15009 


.289 


18814 


.332 


. 22792 


.204 


11504 


.247 


15095 


.29 


18905 


.333 


. 22886 


.205 


11584 


.248 


15182 


.291 


18996 


.334 


. 22980 


.206 


11665 


.249 


15268 


.292 


19086 


.335 


. 23074 


.207 


11746 


.25 


15355 


.293 


19177 


.336 


.23169 


.208 


11827 


.251 


15441 


.294 


19268 


.337 


. 23263 


.209 


11908 


.252 


15528 


.295 


19360 


. 338 


. 23358 


.21 


11990 


.253 


15615 


.296 


19451 


. 339 


. 23453 


.211 


12071 


.254 


15702 


.297 


19542 


.34 


. 23547 


.212 


12153 


.255 


15789 


.298 


19634 


l -341 


. 23642 


.213 


12235 


.256 


15876 


.299 


19725 


.342 


. 23737 


.214 


12317 


.257 


15964 


.3 


19817 


.343 


. 23832 


.215 


12399 


.258 


16051 


.301 


19908 


.344 


. 23927 


.216 


12481 


.259 


16139 


.302 


20000 


.345 


. 24022 


.217 


12563 


.26 


16226 


.303 


20092 


.346 


.24117 


.218 


12646 


.261 


16314 


.304 


20184 


.347 


.24212 


.219 


12729 


.262 


16402 


.305 


20276 


.348 


. 24307 


.22 


12811 


.263 


16490 


.306 


20368 


.349 


. 24403 


.221 


12894 


.264 


16578 


.307 


20460 


.35 


. 24498 


.222 


12977 


.265 


16666 


.308 


20553 


.351 


. 24593 


.223 


13060 


.266 


16755 


.309 


20645 


.352 


. 24689 


.224 


13144 


.267 


16843 


.31 


20738 


.353 


. 24784 


.225 


13227 


.268 


16932 


.311 


20830 


.354 


. 24880 


.226 


13311 


.269 


17020 


.312 


20923 


.355 


. 24976 


.227 


13395 


.27 


17109 


.313 


21015 


. 356 


. 25071 


.228 


13478 


.271 


17198 


.314 


21108 


. 357 


.25167 


.229 


13562 


.272 


17287 


.315 


21201 


.358 


. 25263 


.23 


13646 


.273 


17376 


.316 


21294 


.359 


. 25359 


.231 


13731 


.274 


17465 


.317 


21387 


.36 


. 25455 


.232 


13815 


.275 


17554 


.318 


21480 


.361 


. 25551 


.233 


13900 


.276 


17644 


.319 


21573 


.362 


. 25647 


.234 


13984 


.277 


17733 


.32 


21667 


.363 


. 25743 


.235 


14069 


.278 


17823 


.321 


21760 


.364 


. 25839 


.236 


14154 


.279 


17912 


.322 


21853 


.365 


. 25936 


.237 


14239 


.280 


18002 


.323 


21947 


.366 


. 26032 


.238 


14324 


.281 


18092 


.324 


22040 


.367 


.26128 


.239 


14409 


.282 


18182 


.325 


22134 


.368 


. 26225 


.24 


14494 


.283 


18272 


.326 


22228 


.369 


. 26321 


.241 


14580 


.284 


18362 


.327 


22322 


.37 


.26418 


.242 


14666 


.285 


18452 


.328 


22415 


.371 


.26514 



THE BOILER 

TABLE 1 9 — Contin tied 



321 



Ratio 


Area 


Ratio 


Area 


Ratio 


Area 


Ratio 


Area 


.372 


.26611 


.405 


. 29827 


.438 


.33086 


.471 


.36373 


.373 


. 26708 


.406 


. 29926 


.439 


.33185 


.472 


.36471 


.374 


. 26805 


.407 


.30024 


.44 


. 33284 


.473 


.36571 


.375 


.26901 


.408 


.30122 


.441 


.33384 


.474 


.36671 


.376 


. 26998 


.409 


.30220 


.442 


. 33483 


.475 


.36771 


.377 


. 27095 


.41 


.30319 


.443 


.33582 


.476 


.26871 


.378 


.27192 


.411 


.30417 


.444 


.33682 


.477 


.36971 


.379 


. 27289 


.412 


.30516 


.445 


.33781 


.•478 


.37071 


.38 


. 27386 


.413 


.30614 


.446 


. 33880 


.479 


.37171 


.381 


. 27483 


.414 


.30712 


.447 


.33980 


.48 


.37270 


.382 


. 27580 


.415 


.30811 


.448 


.34079 


.481 


.37370 


.383 


. 27678 


.416 


.30910 


.449 


.34179 


.482 


.37470 


.384 


. 27775 


.417 


.31008 


.45 


.34278 


.483 


.37570 


.385 


. 27872 


.418 


.31107 


.451 


.34378 


.484 


.37670 


.386 


. 27969 


.419 


.31205 


.452 


.34477 


.485 


.37770 


.387 


. 28067 


.42 


.31304 


.453 


.34577 


.486 


.37870 


.388 


.28164 


.421 


.31403 


.454 


.34676 


.487 


.37970 


.389 


. 28262 


.422 


.31502 


.4*5 


.34776 


.488 


.38070 


.39 


. 28359 


.423 


.31600 


.456 


.34876 


.489 


.38170 


.391 


. 28457 


.424 


.31699 


.457 


.34975 


.49 


.38270 


.392 


. 28554 


.425 


.31798 


.458 


.35075 


.491 


.38370 


.393 


. 28652 


.426 


.31897 


.459 


.35175 


.492 


. 38470 


.394 


. 28750 


.427 


.31996 


.46 


.35274 


.493 


.38570 


.395 


. 28848 


.428 


.32095 


.461 


. 35374 


.494 


. 38670 


.396 


. 28945 


.429 


.32194 


.462 


. 35474 


.495 


.38770 


.397 


. 29043 


.43 


.32293 


.463 


. 35573 


.496 


. 38870 


.398 


.29141 


.431 


.32392 


.464 


.35673 


.497 


. 38970 


.399 


. 29239 


.432 


.32941 


.465 


.35773 


.498 


. 39070 


.4 


. 29337 


.433 


. 32590 


.466 


. 35873 


.499 


.39170 


.401 


. 29435 


.434 


.32689 


.467 


.35972 


.5 


.39270 


.402 


. 29533 


.435' 


.32788 


.468 


.36072 






.403 


.29631 


.436 


.32887 


.469 


.36172 






.404 


. 29729 


.437 


.32987 


.47 


.36272 







diameter of the circle. Then find the decimal opposite 
this ratio in the column headed "Area." Multiply this 
area by the square of the diameter. The result is the 
required area. 

Example. Diameter of circle = 72 in. Height of 
segment = 25 in. 25 + 72 = .347, which will be found in 
the column headed "Ratio," and the area opposite this 



5WI ENGINEERING 

is .24212. Then .24212x72x72=1,255 sq. in., area 
of segment. 

A boiler is 66 in. in diameter, the working pressure 
is 100 lbs. per sq. in. The distance from the top row 
of tubes to the shell is 25 in. Required, the number 
of diagonal crow foot braces that will, be needed to 
support the heads above the tubes, also the sectional 
area of each brace. The thickness of the heads is ^ 
in. and the T.S. = 55,000 lbs. per sq. in. 

Assume the head to be sufficiently strengthened by 
the flange for a distance .of 2 in. from the shell, the 
diameter of the circle of which the segment above the 
tubes requires to be stayed is reduced by 2 + 2 = 4 in. 
and will therefore be 66 — 4 = 62 in. The rise or height 
of the segment above the tubes is 25-4 = 21 in. 
Required, the area.* 21 -5- 62 = .338. Looking down 
the column headed "Ratio" in Table 19, area opposite 
.338 is .23358. Area of segment = .23358 x 62 x 62 = 
897.88 sq. in. The total pressure on this area will be 
897.88 x 100 = 89,788 lbs. 

Assume the braces to be made of \}i in. round steel 
having a T.S. of 50,000 lbs. per sq. in. and to be 
designed in such a manner as to allow for loss of 
material in drilling the rivet holes in the crow feet. 
Each brace will have a sectional area of .994 sq. in., 
and using 8 as a factor of safety, the strength or safe 
holding power of each stay may be found as follows: 
.994x50,000-8 = 6,212 lbs., and the number of stays 
required = 89,788 lbs. (total pressure) divided by 6,212 
lbs. (strength of each stay) = 14 5, or in round numbers 
15. If the stays are made of flat bars of steel the 
sectional area should equal that of the round stays, 
and the dimensions of the crow feet of all stays should 

* See rule for Table 19. 



THE BOILER 323 

be such as to retain the full sectional area of the body 
after the rivet holes are drilled. 

Each stay is connected to the plate by two ^-in. 
rivets, having a T.S. of 55,000 lbs. per sq. in. and a 
shearing strength of 45,000 lbs. per sq. in. These 
rivets are capable of resisting a direct pull of 10,818 
lbs., using 5 as a factor of safety; ascertained as fol- 
lows: 2A x 45,000 ■*- 5 = 10,818 = strength of two rivets. 
They are also subjected to a crushing strain, and the 
resistance to this is DxC-5, which expressed in 
figures is .875 x 90,000 -*- 5 = 15,750 lbs. 

The proper spacing comes next, and is arrived at in 
the following manner: 

Area to be stayed = 897.88 sq. in. 

Number of stays = 15. 

Area supported by each stay = 897.88 ■*- 15 = 59.8 
sq. in. 

The square root of 59.8 = 7.75 nearly, which is the 
distance in inches each way that the stays should be 
spaced, center to center. 

If through stay rods are used in place of diagonal 
braces for staying the boiler under consideration, the 
number and diameter of the rods may be ascertained 
by the following method: 

Assuming the heads to be supported by channel 
bars, as previously described, and that the stays are 
pitched 14 in. apart horizontally and 13 in. vertically, 
each stay would be required to support an area of 14 x 
13=182 sq. in., and the number of stays would be 
897.88- 182 = 4.9, in round numbers 5. See Fig. 107. 
The pressure being 100 lbs. per sq. in., the total stress 
on each stay = 182 x 100 = 18,200 lbs. Assume the 
stay rods to be of soft steel having a T.S. of 50,000 
lbs. per sq. in., and using a factor of safety of 8, the 



3^4 ENGINEERING 

sectional area required for each stay will be found as 
follows: 18,200x8^50,000 = 2.9 sq. in., and the 
diameter will be found as follows: 2.9^.7854 = 3.69, 
which is the square of the diameter, and the square 
root of 3.69= 1.9 in., or practically 2 in. The same 
methods of calculation are applicable to the staying of 
the heads below the tubes, also for stay bolts in fire 
box boilers. 

Strength of Unstayed Surfaces. A simple rule for 
finding the bursting pressure of unstayed flat surfaces 
is that of Mr. Nichols, published in the "Locomotive," 
February, 1890, and quoted by Prof. Kent in his 
"Pocket-book." The rule is as follows: "Multiply the 
thickness of the plate in inches by ten times the tensile 
strength of the material used, and divide the product 
by the area of the head in square inches." Thus, 
Diameter of head = 66 in. 
Thickness of head = $/% in. 
Tensile strength = 55,000 lbs. 
Area of head = 3,421 sq. in. 

$/<& x 55,000 x 10 -5- 3,421 = 100, which is the number 
of pounds pressure per square inch under which the 
unstayed head would bulge. 

If we use a factor of safety of 8, the safe working 
pressure would be 100^8= 12.5 lbs. per sq. in., but as 
the strength of the unstayed head is at best an 
uncertain quantity it has not been considered in the 
foregoing calculations for bracing, except as regards 
that portion of it that is strengthened by the flange. 

In all calculations for the strength of stayed surfaces, 
and especially where diagonal crow foot stays are 
used, the strength of the rivets connecting the stay to 
the flat plate must be carefully considered. A large 
factor of safety, never less than 8, should be used, and 



THE BOILER 325 

the cross section of that portion of the foot of the stay 
through which the rivet holes are drilled should be 
large enough, after deducting the diameter of the hole, 
to equal the sectional area of the body of the stay. 

Dished Heads. In boiler work where it is possible to 
use dished, or "bumped up" heads as they are some- 
times called, this type of head is rapidly coming into 
use. Dished heads maybe used in the construction of 
steam drums, also in many cases for dome-covers, thus 
obviating the necessity of bracing. The maximum 
depth of dish, as adopted by steel plate manufacturers 
April 4, 1901, is y& of the diameter of the head when 
flanged, and if the tensile strength and quality of the 
plate from which the heads are made are the same as 
those of the shell plate, the dished head becomes as 
strong as the shell, provided the head has the same 
thickness or is slightly thicker than the shell plate. 

Welded Seams. A few boiler manufacturers have 
succeeded in making welded seams, thus dispensing 
with the time-honored custom of riveting the plates 
together. A good welded joint approaches more 
nearly to the full strength of the material than can 
possibly be attained by rivets, no matter how correctly 
designed the riveted joint may be. The weld also 
dispenses with the necessity of caulking, and a boiler 
having a perfectly smooth surface inside, such as would 
be afforded by welded seams, would certainly be much 
less liable to collect scale and sediment than would 
one with riveted joints. But in order to make a 
success of welded seams the material used must be of 
the best possible quality, and great care and skill are 
required in the work. 

The Continental Iron Works of Brooklyn, New 
York, exhibited at the St. Louis World's Fair in 1904 



326 ENGINEERING 

a welded steel plate soda pulp digester without a 
single riveted joint. The dimensions of this vessel, 
which may be likened to a cylinder boiler without flues, 
were as follows: Thickness of plate, % in.; diameter, 
9 ft.; length, 43 feet. The heads were dished to the 
standard depth. The safe working pressure was 125 
lbs. per sq. in. It appears not only possible, but 
probable, that the process of welding boiler joints may 
in time supplant the older custom of riveting. 



CHAPTER II 

CARE OF THE BOILER 

Washing out the boiler — Duties of the boiler washer — How to pre- 
pare a boiler for washing — How to clean and inspect the 
inside of a boiler— Fusible plugs — Advantage of manholes, 
giving free access to top and bottom of boiler — Responsibility 
resting upon the boiler washer — Necessity of keeping water 
column clean — Scraping the flues — Fire cracks and how to 
deal with them — Firing up and how it should be done — Danger 
in too sudden heating up of a boiler — Advantages of filling a 
recently washed out boiler with warm water — Connecting 
with the main header and the safest method of procedure. 

Washing Out. In order to get the best results from 
the burning of coal or any other fuel in a boiler furnace 
it is absolutely necessary to keep the boiler as clean as 
possible, both Inside and outside. In large plants the 
boiler washer and his helper are detailed to look after 
this part of the work, and while the job is by no means 
a very desirable one, it is at the same time a very 
responsible one, and much depends upon the thorough- 
ness with which the work is done. In small plants, 
consisting of one or two boilers, the engineer generally 
has to attend to the details of the work himself, and 
no matter whether the plant be large or small, the 
engineer in charge is the man above all others who 
should be most interested in seeing that thorough 
work is done, not only as a matter of safety, but for 
the sake of his reputation as an engineer. The boiler 
that is to be washed out should be allowed to gradually 
cool for ten or twelve hours. It will then be in a 
condition which will permit a man to go inside of it ' 
327 



328 ENGINEERING 

and do effective work, and no boiler can be thoroughly- 
cleaned and inspected unless the boiler washer does 
go inside. 

These remarks apply, of course, to horizontal tubular 
or flue boilers and water tube boilers having drums 
large enough for a man to crawl into. Some types of 
internally fired boilers are provided with man-holes, 
but the majority of them have only hand-holes into 
which the hose for washing out may be inserted. 

After the water has been allowed to run out, the first 
step in washing out a boiler is to remove all the loose 
mud and scale possible by means of a steel scraper 
fitted to a long handle and introduced through the 
man-hole in the bottom part of the head. This will 
prevent the scale from getting into the blow-off pipe 
and stopping the flow of the water used for washing 
the boiler. If there is a man-hole on top, the next 
thing in order is to take the hose in through it and 
give the sides of the shell and also the tubes a good 
cleaning. 

Sometimes it happens that where an exhaust heater 
of the open type is used, oil will find its way into the 
boiler and, mixing with the mud, will form a thick 
pasty-like substance on the sides of the boiler along 
the water line. This should be carefully scraped off 
and removed, as any matter containing oil or grease is 
a very dangerous thing to have inside a boiler. 

After cleaning the upper part of the boiler, it should 
be inspected for loose braces or rivets. This can best 
be accomplished by tapping the parts with a light 
hammer. A solid rivet will give a clear metallic 
sound, and a little practice will enable one to easily 
detect the sound of a loose brace or broken rivet. 

Signs of corrosion or pitting of the shell along the 



CARE OF THE BOILER 329 

water line should also be carefully searched for. 
Fusible plugs, to be effective, must be kept clean, and 
the only opportunity for cleaning them is at the time 
of washing out the boiler. Therefore while working on 
the upper part of the boiler, attention should be given 
to the fusible plug. If it is one of the ordinary kind, 
screwed into the back head above the tubes, it should 
be taken out and cleaned and before replacing it the 
thread should be well coated with a mixture of cylinder 
oil and plumbago, which will prevent it from sticking. 
If the fusible plug is one of the type consisting of a 
brass tube extending from the top of the shell to the 
water level, the lower end of this tube should be 
cleaned of all mud or scale. 

Having thus finished above the tubes, the mud and 
scale should again be scraped from the bottom, after 
which the hose should be inserted through the front 
man-hole that should be in every horizontal boiler. 

Some authorities argue that a man-hole should not 
be cut in the bottom part of a boiler head, giving as 
their reason that it weakens the head, but the logic is 
not sound, for the reason that the man-hole can be 
reenforced in such a manner as to make it fully as 
strong as the solid sheet, and when we consider the 
great advantage of having a man-hole in the bottom, 
both as- regards washing out and also for repairs, it is 
plain that it is really a necessity. 

After washing out all the loose mud and scale that 
it is possible to get from the bottom, the boiler washer 
should next go inside and, with scrapers and tools 
made for the purpose, he should scrape and chip off 
all the scale that he can from the bottom, because 
there is where lies the greatest danger from burnt 
sheets caused by accumulations of scale preventing the 



330 ENGINEERING 

water from getting to the metal. Much good work 
may be accomplished in this way and no boiler washer 
should consider the job complete until he has gone 
through the boiler both top and bottom, and not only 
cleaned but inspected it. Any loose rivets, broken or 
loose braces, signs of corrosion or pitting should be at 
once reported to the chief engineer or superintendent. 

It will thus be seen that great responsibility rests 
with the boiler washer, for the reason that he is the 
man that is in closest touch with the inside of the 
boiler, and it is due to the manner in which he does 
his work inside the boiler whether a defect is discovered 
and repaired in 'time or whether it is allowed to go 
until the result is often a grave disaster. The author 
desires to enter a plea for this hard-worked and too 
often underpaid craftsman, and hereby expresses the 
wish that his services were better appreciated. 

The water column or combination should receive 
particular attention each time the boiler is washed out. 
The lower pipe leading to the boiler is liable to become 
clogged with scale, and if not cleaned regularly it is 
sure to cause trouble by preventing a free flow of the 
water from the boiler to the gauge glass. 

If the boiler is of the horizontal tubular type, the 
tubes should be scraped inside, and with water tube 
boilers use the steam jet to blow the soot and ashes 
from between the tubes. Soot, in addition to choking 
the draft, is also a non-conductor of heat. 

After the hand-hole and man-hole plates have been 
replaced the boiler may be filled with water to the 
proper level, and while this is being done it is in order 
to take a look into the furnace for any broken grates 
or accumulations of clinkers on the side walls or bridge 
wall. These clinkers should be chipped off, also the 



CARE OF THE BOILER 331 

bottom of the boiler should be swept clean of ashes and 
examined for any defects, such as fire cracks about 
the rivets most exposed to the heat. These cracks 
may often exist some time before being discovered 
unless a close inspection is made. They are small 
cracks radiating from the rivet holes outward past the 
rivet heads one-half to three-quarters of an inch, and 
are always liable to extend farther until they become a 
source of danger unless arrested in time. They may 
be closed up sometimes with the caulking tool, but if 
one should be found several inches in length, a hole 
should be drilled at the outer end of the crack and a 
rivet put in. This will generally stop it. Fire cracks 
occur in the girth seams only, and especially the seam 
nearest the fire. 

It is essential that the bridge walls of horizontal 
boilers be kept in good repair, in order that as much 
fire brick surface as possible may be exposed to the 
heat. This will greatly aid combustion and prevent 
smoke. 

• Firing Up. After the boiler washer has completed 
his task the next thing in order is firing up, and in 
doing this if care and good judgment are not exercised 
there is danger of doing much damage to the boiler, 
especially if it has been filled with cold water. A 
very light fire should be started at first and kept that 
way until the water gets to the boiling point at least, 
after which the fire may be gradually increased until 
the steam gauge shows a few pounds pressure, when it 
will be safe to urge the fire still more. The bad effects 
resulting from the unequal expansion or contraction 
of the sheets and undue stress upon the rivets, all 
caused by rapid changes of the temperature of the 
boiler from hot to cold or vice versa, cannot be 



36% ENGINEERING 

guarded against too carefully, and they are liable to be 
brought about in two ways: first, by haste in cooling 
down a hot boiler that is to be washed out, and 
secondly, by starting a heavy fire under a cold boiler. 
That part of the boiler most exposed to the heat will 
become hot while other parts farthest removed from 
the fire may still be cold. Very often there is a 
difference of 150 or 200 in the temperature of 
different parts of the boiler for a time during the firing 
up process, and the same dangerous conditions may be 
caused also by blowing all the water out of a boiler 
while under a pressure of 15 or 20 lbs., as is the custom 
of some persons when preparing a boiler for washing 
out. Either custom cannot be too strongly condemned. 

Sometimes a boiler is needed in a hurry after having 
been washed out, and in such an emergency it should 
be filled with warm water; in fact, it is better to always 
fill a boiler with warm water if it is possible to do so 
after washing out. 

Connecting with the Main Header. When the gauge 
shows a pressure that is within 10 or 15 lbs. of being 
the same as that carried on the other boilers it should 
be watched closely, and when the pressure becomes 
the same as that in the main the connecting valve 
should be opened slightly, just sufficient to allow a 
light flow of steam through it, which can be easily 
detected by placing the ear near the valve chamber. 
This steam may be passing from the boiler to the 
header or vice versa, but whichever way it is going the 
valve should not be opened any farther until the pres- 
sure in the main pipe and in the boiler is equalized, 
when it will be found that the valve may be opened 
easily. While connecting the boiler the dampers 
should be closed. 



CARE OF THE BOILER 333 

Care should always be exercised in connecting a 
recently fired up boiler, "and the engineer should be 
certain that the steam gauge and pop valve are in 
good working order. Otherwise there is liability of a 
serious accident occurring, either in breakage of the 
steam pipe, or what is still worse, a boiler explosion. 



CHAPTER III 
MECHANICAL STOKERS 

Principles involved in the action of automatic stokers — Advan- 
tages and disadvantages attending their use— Classification 
and general description of stokers — Coal-handling machinery 
— Under-feed stokers — Mansfield chain grate stoker — Play ford 
stoker — Vicars mechanical stoker — The Wilkinson stoker- 
Murphy stoker — Roney stoker— The American under-feed 
stoker — The Jones under-feed stoker — Outside furnaces — Con- 
ditions required in a boiler furnace to ensure good combus- 
tion — Hindrances to good combustion — Description of Burke 
' outside furnace. 

The principles governing the operation of mechan- 
ical or automatic stokers are in the main correct, viz., 
that the suppl}' of coal and air is continuous and. that 
provision is made for the regulation of the supply of 
fuel according to the demand upon the boiler for 
steam; also that the intermittent opening and closing 
of the furnace doors, as in hand firing, thereby 
admitting a large volume of cold air directly into the 
furnace on top of the fire, is avoided. 

Mechanical stokers have within the last twelve years 
been largely adopted in the United States, especially 
in sections where bituminous coal is the principal fuel. 
The disadvantages attending their use are: 

First, that the cost of properly installing them is so 
great that their use is practically prohibited to the 
small manufacturer. 

Second, that in case of a sudden demand upon the 
boilers for more steam the automatic stoker cannot 
respond as promptly as in hand firing, although 
334 



MECHANICAL STOKERS 33.5 

this objection could no doubt be met by skillful 
handling. 

Third, the extra cost for power to operate them, 
although this is probably offset by the diminished 
expense for labor required, as compared to hand firing. 

There are many different types of mechanical stokers 
and automatic furnaces, but they may for convenience 
be grouped into four general classes. In class one the 
grate consists of an endless chain of short bars that travel 
in a horizontal direction over sprocket wheels, operated 
either by a small auxiliary engine or by power derived 
from an overhead line of shafting in front of the boilers. 

In class two may be included stokers having grate 
bars somewhat after the ordinary type as to length and 
size, but having a continuous motion up and down or 
forward and back. This motion, though slight, serves 
to keep the fuel stirred and loosened, thus preventing 
the firing from becoming sluggish. The grate bars in 
this class of stokers are either horizontal or inclined at 
a slight angle, and their constant motion tends to 
gradually advance the coal from the front to the back 
end of the furnace. 

Class three includes stokers having the grate bars 
steeply inclined. Slow motion* is imparted to the 
grates, the coal being fed onto the upper end and 
forced forward as fast as required. 

Class four includes an entirely different type of 
stoker, in that the fresh coal, is supplied underneath 
the grates, and is pushed up through an opening left 
for the purpose midway of the furnace. The gases, on 
being distilled, immediately come in contact with the 
hot bed of coke on top and the result is good com- 
bustion. In this type of stoker steam is the active agent 
used for forcing the coal up into the furnace, either 



336 



ENGINEERING 



••;.-: 






MECHANICAL STOKERS 



337 



by means of a long, slowly-revolving screw, as in the 
American stoker, or a steam ram, as with the Jones 
under-feed stoker. A forced draft is employed, and 
the air is blown into the furnace through tuyeres 
When these stokers are intelligently handled they 
give good results, especially with cheap bituminous 
coal. The clinker formed on the grate bars or dead 
plates is easily removed. 

The coal is supplied to mechanical stpkers either by 
being shoveled by hand into hoppers in front of and 
above the grates, or, as 
is the case in most of 
the large plants using 
them, it is elevated by 
machinery and depos- 
ited in chutes, through 
which it is fed to 
each boiler by gravity. 
Stokers of the chain 
grate variety are usu- 
ally constructed so that 
they may be withdrawn 
from underneath the 
boiler in case repairs are 
necessary. The coal, 
either nut or screen- 
ings, is fed into a hop- 
per in front of and 
above the level of the grate 
along towards the rear end. 




FIGURE 112. 

CAHALL VERTICAL BOILER WITH 

CHAIN GRATE STOKER ATTACHED 



and is slowly carried 
The ash drops from 
the grate as it passes over the sprocket wheel at 
the rear. 

Fig. in shows a battery of Babcock and Wilcox 
water tube boilers fitted with chain grate stokers. The 



838 



ENGINEERING 



buckets for elevating the coal to bins overhead, from 
whence it is fed by gravity to the stokers, are not 
shown. These buckets or carriers may also be utilized 
for conveying the ashes from the boiler-room. 




O H 
K g 



Fig. 112 is a sectional view of a vertical Cahall 
boiler with a Mansfield chain grate stoker, and Fig. 113 
shows the same stoker withdrawn from the boiler. 

The Coxe mechanical stoker operates upon the same 



MECHANICAL STOKERS 



339 



general principles as do those previously described, 
being of the chain grate type, but it has in addition a 
series of air chambers just underneath the upper 
traveling grate. These air chambers are made of sheet 
iron and are open at the top and provided with dampers 
for regulating the air pressure for different sections of 
the grate. The air blast is supplied by a fan. Another 
featureof this stoker is a water chamber for the bottom 
section of the grate to travel through on its return. 




FIGURE 114. 



The Playfor.d stoker has wrought iron T bars extend- 
ing across the furnace and attached to the traveling- 
chains. These T bars carry the small cast iron sections 
composing the grate. A screw conveyor is also 
placed in the ash pit for the purpose of carrying the 
ashes from the rear to the front of the pit. Fig. 114 is 
a sectional view of the Playford stoker attached to a 
water tube boiler. 

In class two may be included stokers having the 
grates inclined more or less. In some varieties the 
grates incline from front to rear, while in others they 



340 ENGINEERING 

are made to incline from the side walls towards the 
center line of the furnace. 

In the Vicars mechanical stoker the grate bars are 
somewhat of the shape of the ordinary grate and lie in 
two tiers in a horizontal position. The lower or back 
tier next the bridge wall is stationary and is placed 
there for the purpose of catching what coal is carried 
over the ends of the upper or moving grate bars. 
These have a slow reciprocating motion which 
gradually moves the hot coke back towards the bridge 
wall The coal is fed from a hopper into two com- 
partments, from which it is pushed by reciprocating 
plungers onto a coking plate and from thence it 
passes to the grate bars. The motion of these bars 
has several intermediate variations, from a state of. 
rest to a movement of 3^ in. They have a simul- 
taneous movement forward by which the fuel is 
advanced, but on the return movement the bars act at 
separate intervals. In this manner the fuel remains 
undisturbed by the return motion of the grates. Fig. 
115 illustrates this stoker. 

In the Wilkinson stoker, Fig. 116, the grate bars 
are hollow and are set at an angle of 20°, the inclina- 
tion being from front to back. Each bar is stepped 
along its fire surface and on the rise is perforated with 
a long, narrow slot. A steam pipe extends along the 
front of the furnace and from this pipe small branch 
pipes lead into the ends of the grate bars, which latter 
are in fact a series of hollow trunks with their front 
ends open. When in operation a steam blast is 
admitted to each of the several trunk grate bars 
through the small branch pipes, and this blast induces 
an air current of more or less pressure, which finds an 
outlet through the narrow slots in the stepped fire 



MECHANICAL STOKERS 



341 



surface of the grates and directly into and through the 
burning mass of fuel. A slow reciprocating motion is 
imparted to the grates by means of cranks and links 
operated from an overhead shaft; see Fig. 117, These 
cranks are set alternately at 90° with each other, thus 
giving a forward movement to one-half of the grate 
bars while at the 
same time the 
other half is 
moving back- 
ward. In this 
manner the fuel 
is kept slowly 
moving down 
the inclined 
grates. 

The Murphy 
Automatic Fur- 
nace, a sectional 
view of which is 
shown in Fig. 
1 1 8, has the 
grates inclined 
inwards from 
the side walls, 
while a fire 
brick arch is 
sprung from 




FIGURE 115. 



side to side to cover the entire length of the grate. 
The coal is shoveled or fed by carrier into the 
coal magazines, one on each side, as shown in the 
cut If the furnace is placed directly under the boiler 
it necessitates putting these coal magazines within the 
side walls, but as the Murphy furnace is usually con- 



342 



ENGINEERING 



structed at the present day as an outside furnace, the 
coal magazines are independent of the boiler walls. 
The bottom of each magazine is used as a coking 




plate, against which the upper ends of the inclined 
grates rest. On the central part of this plate is an 
inverted open box. This is termed the "stoker box," 



MECHANICAL STOKERS 



343 



and it is moved back and forth across the face of the 
coking plate by means of a shaft with pinions that 
mesh into racks under each end of the box. By means 




FIGURE 117. WILKINSON STOKER. 

of this motion of the stoker boxes the coal is pushed 
forward to the edge of the coking plate and from 
thence it slowly passes down over the inclined grates 



344 



ENGINEERING 



toward the center of the furnace. At this point [he 
slowly rotating clinker breaker grinds the clinker and 
other refuse and deposits them in the ash pit. 




1 1 1 1 I-. 1 1 


1 j 1 1 1 1 


1 ' 1 1 1 1 1 


! 1 1 1 J 1 






' IPIT | 1 









FIGURE 118. THE MURPHY AUTOMATIC FURNACE. 



Above the coking plates are the "arch plates," upon 
which the bases of the fire brick arch rest. These 
plates are ribbed, the ribs being an inch apart, and, the 
arch resting upon these ribs, there is thus provided a 
series of air ducts by means of which the air, already 
heated by having been admitted in front and passed 
through the flues over the arch, is conducted into the 
furnace above the grates and comes directly in contact 
with the gases rising from the coking fuel. Air is also 
admitted under the coking plate and, passing up 
through the grates, serves to keep them cool and also 
furnishes the needed supply to the burning coke as it 
slowly moves down toward the center. 



MECHANICAL STOKERS 345 

The fuel is aided in its downward movement by the 
constant motion of the grates, one grate of each pair 
being moved up and down by a rocker at the lower 
end. 

Motion is imparted to the various moving parts of 
this furnace by means of a reciprocating bar extending 
across the outside of the entire front, and to which all 
the working parts are attached by links and levers. 
This bar is operated by a small engine at one side of 
the setting, the power required being about one horse- 
power per furnace. 

The Roney stoker consists of a set of rocking stepped 
grate bars, inclined from the front towards the bridge 
wall. The angle of inclination is 37 . A dumping 
grate operated by hand is at the bottom of the incline 
for the purpose of receiving and discharging the clinker 
and ash. This dumping grate is divided into sections 
for convenience in handling. 

The coal is fed onto the inclined grates from a 
hopper in front. The grate bars rock through an arc 
of 30 , assuming alternately the stepped and the 
inclined position. Fig. 119 is a sectional perspec- 
tive view of this stoker and illustrates the working 
parts. 

The grate bars receive their motion through the 
medium of a rocker bar and connecting rod. A shaft 
extending across the front of the stoker under the 
coal hopper carries an eccentric that gives motion to 
the connecting rod and also to the pusher in the coal 
hopper. This pusher, working back and forth, feeds 
the coal over the dead plate onto the grates," and its 
range of motion is regulated by a feed wheel from no 
stroke to full stroke, according to the demand for coal. 
The motion of the grate bars may also be regulated by 



340 



ENGINEERING 



a sheath nut working on a long thread on the connect- 
ing rod. Each grate bar consists of two parts, viz., a 
cast iron web fitted with trunnions on each end that 
rest in seats in the side bearer and a fuel plate having 
the under side ribbed to allow a free circulation of 
air. 

The fuel plate is bolted to the web and carries the 




FIGURE 119. 

SECTTONAL PERSPECTIVE OF THE RONEY MECHANICAL STOKER. 



fuel. The grates lie in a horizontal position across 
the furnace in the form of steps, and ample provi- 
sion is made for the admission of air through the 
slotted webs. A fire brick arch is also sprung 
across the furnace, covering the upper portion of the 
grate. 

This arch, being heated to a high temperature, serves 
in a measure to partly coke the coal as it passes under 
it. Air is also admitted on top of the coal at the 
front. This air is heated by its passage through a 
perforated tile over the dead plate and adjoining the 



MECHANICAL STOKERS 



347 



fire brick arch. Fig. 120 shows the location of the 
arch and tile. 

In mechanical stokers of the uncler-feed type the air 
is supplied by forced draft. 

The American stoker consists of a horizontal con- 
veyor pipe into which the coal is fed from a hopper. 
The diameter cf this pipe depends upon the quantity 
of coal to be burned, and varies from 4% in. for the 
smaller sizes up to 9 and 10 in. for the larger sized 
stokers. The length of the conveyor pipe for the 




figure 120. 

standard 10-in. stoker is 72 in. Attached to the outer 
end of this conveyor pipe, and forming a part of it, is 
an iron box containing a reciprocating steam motor 
which, through the medium of a rocker arm and pawl 
and ratchet wheel, drives a screw conveyor shaft that 
slowly revolves within the pipe, thus forcing the coal 
forward and up through another box or trough, which 
latter is wholly within the furnace. Extending around 
the top edges of this box, and on a level with the grate 
bars, there is a series of tuyeres through which the air 
is forced. 



348 



ENGINEERING 



These tuyeres, being at a high temperature, serve to 
heat the air in its passage through them, thus greatly 




■ p g 



^fe:,l 



aiding combustion. Fig. 121 is a longitudinal sectional 
view of this stoker. 

The speed of the screw conveyor is regulated by the 
hand throttle of the motor, according to the demand 



MECHANICAL STOKERS 



349 



for coal. With the 9-in. standard stoker from 350 to 
1,200 lbs. of coal per hour may be burned. Fig. 122 
is a view of the American stoker before being placed 
in position in the furnace. 





\y 




z 


O^^ 


)L 




d 


£j>oo 








g-^S 












w 


11 "?<2-r 






5! 


OOoi^ 






ffi 


^^oS 






£ 


6 'S*§ S 








o'S 


ps 




OS 


£ ^, j»£ 






O 


<<6 




9 


£ 


\4kzc 




■ U- 


GO 


X 






Q 


■53.0 s 






















O 


• x> J; - 






iz 










S-2 






E-* 








CO 


■3 '3 "3 



o i>> S fl -^ 
O O 3 j^> 



The air jets, passing out from the tuyeres in- a 
horizontal direction, and from opposite sides, cut 
through the rounded bed of coal and the gases are thus 
ignited and consumed immediately after being distilled 



350 ENGINEERING 

from the coal, while the pressure of the coal- rising 
from underneath forces the already coked fuel over the 
edges of the trough or box onto the grates which 
occupy the space between^ the side walls and the coal 
trough. The air is first delivered from the fan into 
the air box that surrounds the coal trough on three 
sides and from thence it passes to the tuyeres. If this 
stoker is properly handled very good results may be 
obtained by its use, but, like all other devices for burn- 
ing coal under boilers, it is bad policy to endeavor to 
force it beyond its capacity. 

In the Jones under-feed stoker the coal is pushed for- 
ward and up into the furnace through a cast iron retort or 
trough. The impelling force is a steam ram connected 
to the outer end of the retort, and the speed of the ram is 
regulated automatically by the steam pressure, or by 
hand as desired. The coal is supplied to the ram through 
a cast iron hopper having a capacity of 125 to 140 lbs. 

Forced draft is also employed in this stoker, the air 
being conducted from the fan or blower through 
galvanized iron pipes into the closed ash pit, which 
really forms an air box, as the space on either side of 
the retort that is usually occupied by grate bars is in 
this case covered by solid cast iron dead plates upon 
which the coked fuel lies until it is consumed. These 
plates, being hot, serve to heat the air coming in con- 
tact with them in its passage to the cast iron tuyeres 
through which it passes to the bed of burning fuel in 
the retort. Air entirely surrounds the retort on the 
sides and back end, and is at a constant pressure in 
the ash pit, but can only pass into the furnace through 
the tuyeres, the jets of air cutting through the rounded 
heap of incandescent fuel from opposite sides and in 
a direction inclined upwards. 



MECHANICAL STOKERS 



351 



Coal is supplied to the hopper either by hand, or by 
mechanical means where the plant is fitted with coal- 
handling machinery. The opening through which it 
passes from the hopper to a position in front of the 
ram is 8 x 10 in. in size. Each charge of the steam 




FIGURE 123. 

ram carries forward 15 to 20 lbs. of coal. Connected 
to the ram and moving in conjunction with it is a long 
rod extending through the retort near the bottom. 
Upon this rod are carried shoes that act as auxiliary 
plungers and facilitate the movement of the coal. 




FIGURE 124. 



Fig. 123 is a sectional view of the Jones stoker, 
showing the machine full of coal, with the ram ready 
to make a charge. Fig. 124 shows the stoker complete 
before being placed in the furnace. 



352 ENGINEERING 

It is claimed by the builders of under-feed stokers, 
and the claim appears to have good foundation, that 
by pushing the green coal up so as to meet the upper 
crust of glowing fuel the gases on being distilled 
immediately come in contact with and are consumed 
by the burning mass, and the formation of smoke is 
thus prevented. Both the Jones under-feed and the 
American stokers have proved to be very successful in 
the burning of the cheaper bituminous coals of the 
West. One feature tending to commend them is the 
fact that practically all of the coal is utilized, there 
being no waste caused by the slack coal or fine screen- 
ings dropping through the grate bars into the ash pit 
unconsumed. 

A good substitute for the mechanical stoker is an 
outside furnace, by which is meant a boiler installation 
having the furnace in front of instead of underneath 
the boiler. One of the principal hindrances to good 
combustion in the ordinary type of boiler furnace is 
the fact that the temperature of the boiler shell or 
water tubes with which the gaseous products of com- 
bustion come in contact can never be higher than the 
temperature of the water contained within the boiler. 
This temperature ranges from 297° for steam at 50 lbs. 
gauge pressure, up to 407° for 255 lbs. pressure, while 
the temperature of the furnace, according to Dr. 
Thurston and other high authorities, ranges from 2,010° 
to 2,550°. 

It is evident that perfect combustion does not take 
place until these high temperatures are reached. Each 
time the furnace is charged with fresh coal, especially 
if the boiler be hand-fired, a large volume of volatile 
gases is liberated but not consumed. If these gases 
are allowed to immediately come in contact with a 



MECHANICAL STOKERS 



353 



comparatively cool surface, as for instance the heating 

surface of the boiler, the result is a cooling of the 

gases, incomplete combustion and the formation of 

smoke and soot. If on the other hand the furnace is 

so constructed that these gaseous products first impinge 

against hot surfaces, such as fire brick arches or bafflers 

that have a temperature 

corresponding to that 

of the furnace, good 

combustion is assured. 

This condition is in a 

large degree attained 

by the use of outside 

furnaces that permit the 

construction of a fire 

brick arch to cover the 

entire grate surface. 

The Burke furnace, 
patented by James V. 
Burke of Chicago, is a 
notable example of this 
type of furnace. It is 
applicable to any type 
of stationary boiler. 
Fig. 125 shows this fur- 
nace as applied to 
tubular boilers. It con- 
sists of a fire brick arch 
extending from 6 to 8 
ft. outwards from the boiler front and of a width to 
correspond to the diameter of the boiler. The arch 
rests securely upon brick work inclosed in a well 
ventilated iron casing. There is practically no heat 
radiated from this furnace, all the heat generated 




Front View. 

FIGURE 125. 



354 



ENGINEERING 



by it passing to the boiler. The central portion of the 
grate bars consists of shaking grates, while the side 
bars are stationary and inclined. 

Fig. 126 is a sectional view and will serve to illustrate 
the construction of this furnace. The coal is fed 
through pockets on top on each side of the arch, the 
larger furnaces having two pockets on each side and 
the smaller sizes one. The doors in front are only 




C/foss Seer; 0//. 
FIGURE 126. 

opened for the purpose of cleaning fires or when first 
starting fires. The air is supplied by way of the ash 
pit, passing up through the grate bars. A portion of 
the air supply is also drawn through the ventilators and 
passes to the upper part of the furnace. The arch 
extends under the front end of the boiler 6 or 8 in. , and 
there is a bridge wall about 4 ft. back from the front 
against which the gases from the furnace impinge. 
There are 42 sq. ft. of grate surface in the larger 



MECHANICAL STOKERS 355 

sizes, and 22 sq. ft. in the smaller size. Good com- 
bustion is attained in this furnace, owing to the fact 
that the gases as they are distilled from the coal come 
immediately in contact with the highly heated surface 
of the arch directly over the fire, 



CHAPTER IV 
THE STEAM TURBINE 

The steam turbine — Lack of information concerning steam tur- 
bines — Points of difference between the turbine and the 
reciprocating engine — Kinetic energy in steam — Hero's steam 
turbine — Branca's steam turbine — Fundamental principles of 
the steam turbine — Types of steam turbines built in the 
United States — The Westinghouse-Parsons turbine — Theo- 
retical velocity of steam exhausting into a vacuum — Relation 
of bucket speed to steam speed — Speed of the Westinghouse- 
Parsons turbine — Description of cylinder and blades — Rela- 
tion of stationary to moving blades — Curvature of blades — 
Action of the steam within the turbine explained — Balancing 
pistons — Construction of bearings — A floating journal — Lubri- 
cation of bearings — Water seal packing — Speed regulation — 
Description and diagram of governor — Efficiency of steam 
turbines — Tests of Westinghouse-Parsons turbines. 

Although the turbine principle of utilizing the energy 
in steam and converting it into useful work has been 
experimented upon for many years, it is only since the 
inauguration of the twentieth century that steam 
turbines have been brought to the front as efficient 
power producers. 

There are to-day in this country four distinct types 
of steam turbines, each one of which has its own 
characteristic features distinguishing it from the 
others, but in each the kinetic energy and velocity of 
the expanding steam constitute the source of power. 

Notwithstanding the fact that much has been said 

and written during the past four years regarding the 

steam turbine, the machine is to-day a mystery to 

thousands of engineers, not because they do not desire 

356 



THE STEAM TURBINE 



357 



information upon the subject, but because of a lack of 
opportunities for obtaining that information. The 
author therefore considers that a space devoted to 
this subject would no doubt be of benefit to his 
readers. 
The piston of the reciprocating engine is driven back 




FIGURE 127. 



and forth by the static expansive force of the steam, 
while in the steam turbine not only the expansive force 
is made to do work, but a still more important element 
is utilized, viz., the kinetic energy or heat energy 
latent in the steam and which manifests itself in the 
rapid vibratory motion of the particles of steam 



358 



ENGINEERING 



expanding from a high to a lower pressure, and this 
motion the steam turbine transforms into work. 

One of the earliest descriptions of a device for con- 
verting the power of steam into work was recorded by 
Hero, a learned writer who flourished in the city of 
Alexandria in Egypt, in the second century before 
Christ. Hero describes a machine called an ^Eolipile 
or "Ball of yEolus,' 1 illustrated in Fig. 127. B is the 
boiler under which a fire was made. G is a hollow 







.FIGURE 128. 

metallic globe that revolved on trunnions C and D, 
one of which terminated in a pivot at E, while the 
other was hollow and conveyed the steam generated in 
the boiler B to the interior of the globe or ball, from 
which it escaped through the hollow bent tubes H and 
I, and the reaction of the escaping steam caused the 
globe to revolve. This was the first steam turbine, and 
it worked on the reaction principle. 

Many centuries later, in the year A.D. 1629, Branca, 
an Italian, described an engine which marks a change 



THE WESTINGHOUSE PARSONS STEAM TURBINE 359 

in the method of using the steam. Branca's engine 
consisted of a boiler A, Fig. 128, from which the steam 
issued through a straight pipe and impinged upon the 
vanes of a horizontal wheel carried upon a vertical 
shaft, causing it to revolve. This device was the germ 
of the impulse turbine, and these two principles, viz., 
reaction and impulse, either one or the other and 
sometimes a combination of both, are the fundamental 
principles upon which the successful steam turbines of 
the present age operate. 

As previously stated, there are four types of steam 
turbines being manufactured in this country at present, 
viz., 

The Westinghouse-Parsons Turbine, 

The General Electric Curtis Turbine, 

The Hamilton-Holzwarth-Rateau Turbine, and 

The De Laval Turbine. 
Each will be taken up in its regular order and its 
distinctive theoretical features studied. 

The Westinghouse-Parsons Steam Turbine is funda- 
mentally based upon the invention of Mr. Charles A. 
Parsons, who, while experimenting with a reaction 
turbine constructed along the lines of Hero's engine, 
conceived the idea of combining the two principles, 
reaction and impulse, and also of causing the steam to 
flow in a general direction parallel with the shaft of 
the turbine. This principle of parallel flow is common 
to all four types of turbines, but is perhaps more 
prominent in the Westinghouse-Parsons and less so in 
the De Laval. 

A cubic foot of steam under 100 lbs. pressure, if 
allowed to discharge into a vacuum of 28 in., would 
attain a theoretical velocity of 3,860 ft. per second and 
would exert 59,900 ft. -lbs. of energy. A law of turbo 



360 ENGINEERING 

mechanics specifies that in order to obtain the highest 
efficiency in the operation of turbines (whether water 
or steam) the relation between bucket speed and fluid 
speed (steam in this case) should be as follows: 

For purely impulse wheels, bucket speed equals 
one-half of jet speed. 

For reaction wheels, bucket speed equals jet speed. 

Assuming the velocity of the jet of steam issuing 
from the nozzle to be 4,000 ft. per second, this would 
mean a peripheral speed of 2,000 ft. per second for an 
impulse wheel, and for a wheel 1 ft. in diameter the 



figure 129. 

speed would be 38,100 R. P. M. But such a speed is 
beyond the limits of strength of material. 

As before stated, the Westinghouse-Parsons turbine 
operates on both impulse and reaction principles, and 
by a system of compounding, which will be explained 
later on, the peripheral velocity of the machine has 
been so reduced as to bring it within practical limits 
while at the same time the power value of the steam is 
utilized to a high degree of efficiency. 

The speed of the Westinghouse-Parsons turbine 



THE WESTINGHOUSE-PARSONS STEAM-TURBINE 361 

varies from about 750 R. P. M. for a 5,000 K. W. 
machine to 3,600 R. P. M. for a 400 K. W. turbine. 

Fig. 129 is a general view of a 400 K. W. turbine 
generator unit. Fig. 130 shows a 600 H. P. machine 
with the upper half of the cylinder, or stator as it is 
termed, thrown back for inspection. Fig. 131 is a 
sectional view of a Westinghouse-Parsons turbine, and 
it will be noticed that there are three sections or drums, 
gradually increasing in diameter from the inlet A to 




figure 130. 



the third and last group of blades. This arrange- 
ment may be likened in some measure to the triple 
compound reciprocating engine. 

By reference to Fig. 130 it will be seen that t the 
inside of the cylinder is studded with rows of small 
stationary blades and that the rotor or revolving part 
of the machine is also fitted with rows of small blades, 
similar in shape and dimensions to the stationary 



362 



ENGINEERING 



blades. When the upper half of the cylinder is in 
position, each row of stationary blades fits in between 
two corresponding rows of moving blades. This 
arrangement may perhaps be better understood by 
reference to Fig. 132, which illustrates the relation of 
the stationary blades to the moving blades when in 
position, and also shows by the arrows the course of 
the steam and its change of direction caused by the 
stationary blades. 

For the purpose of explanation the moving blades or 




FIGURE 131. 

vanes may be considered as small curved paddles pro- 
jecting from the surface of the rotor, and there is a 
large number of them, as, for instance, taking a 400 
K. W. machine, there are 16,095 moving blades and 
14,978 stationary blades, a total of 31,073. 

The stationary vanes, as previously explained, project 
from the inside surface of the cylinder. Both station- 
ary and moving vanes are similar in shape, and are 
made of hard drawn material, and they are set into 



THE WESTINGHOUSE-PARSONS STEAM TURBINE 363 

their places and secured by a caulking process. The 
blades vary in size from ^ to 7 in. in length, accord- 
ing to where they are used. Referring to Fig. 130, it 
will be observed that the shortest blades are placed at 
what might be termed the steam end of each section or 
drum of the rotor and cylinder, and that their length 
gradually increases, corresponding with the increased 
volume of steam, until a mechanical limit is reached, 
when a new group of blades begins on a succeeding 
drum of larger diameter. Referring to Fig. 132, 
which is a sectional view of four rows of blades, it will 

1 I C^CCCCC^CCC STATIOI 



1 )) )) )) i).l)Tn ^ BLADES 



) )) } ))Jb) )Ti 



STATIONARY BLADES 

MOVING BLADES 



FIGURE 132. 

be noticed that all the blades, whether stationary or 
moving, have the same curvature. Also that the curves 
are set opposite each other. The reason for this will 
be apparent as the diagram is studied. The steam at 
pressure P first comes in contact with row I of station- 
ary blades. It expands through this row, and in 
expanding the pressure falls to P'. 

The energy in the steam is converted into velocity, 
and it impinges upon row 2 of moving blades, driving 
them around in their course by impulse. A second 
expansion now occurs in row 2 and again the energy is 
converted into velocity, but this time the reaction of 



364 ENGINEERING 

the steam as it leaves the blades of row 2 also tends to 
impel them around in their course. The moving 
blades thus receive motion from two causes — the one 
due to the impulse of the steam striking them, and the 
other due to the reaction of the steam leaving them. 

This cycle is repeated in rows 3 and 4, and soon 
throughout the length of the rotor until the exhaust 
end is reached. 

It should be noted that the general direction taken 
by the steam in its passage through the turbine is in 
the form of a spiral or screw line about the rotor. The 
clearance between the blades as they stand in the rows 
is }i in. for the smallest size blades and % in. for the 
larger ones, gradually increasing from the inlet to the 
exhaust. In the 5,000 K. W. machine the clearance at 
the exhaust end between the rows of blades is 1 in. It 
will thus be seen that there is ample mechanical 
clearance, also allowance for lateral motion for adjust- 
ment of the rotor, although this is very slight, as the 
rotor is balanced at all loads and pressures by the 
balancing pistons PPP, Fig. 131, to which reference 
is now made. These pistons revolve within the 
cylinder, but do not come in mechanical contact with 
it; consequently there is no friction. The diameter of 
each piston corresponds to the diameter of one of the 
three drums. 

The steam entering the chamber A through valve V 
presses against the turbine blades and goes through 
doing work by reason of its velocity. It also presses 
equally in the opposite direction against the first piston 
P, and so the shaft or rotor has no end thrust. On leav- 
ing the first group of blades and striking the second 
group the pressure in either direction is again equalized 
by the balance port E allowing the steam to press against 



THE WESTINGHOUSE-PARSONS STEAM TURBINE 365 

the second balance piston P. The same event occurs at 
group three, the steam acting upon the third piston P. 

The areas of the balancing pistons are such that, no 
matter what the load may be or what the steam pres- 
sure or exhaust pressure may be, the correct balance 
is maintained and there is practically no end thrust. 
Below is shown a pipe E connecting the back of the 
balancing pistons with the exhaust chamber. This 
arrangement is for the purpose of equalizing the 
pressure at this point with the pressure in the exhaust 
chamber B. 

It might be thought that the blades, on account of 
their being so light and thin, would wear out very fast, 
but experience so far shows that they do not. This 
may be accounted for in two ways. First, the reduc- 
tion of the velocity of the steam, the highest velocity 
in the Parsons turbine not exceeding 600 ft. a second; 
secondly, the light steam thrust on each blade, said to 
be equal to about 1 oz. avoirdupois. This is far within 
the bending strength of the material. A steam strainer 
is also placed in the admission port, to prevent all 
foreign substances from entering the turbine. 

A rigid shaft and thrust or adjustment bearing 
accurately preserves the clearances, which are larger in 
this turbine than in other types, owing to the fact that 
the entire circumference of the turbine is constantly 
filled with working steam when in operation. 

The bearings shown in Fig. 131 are constructed 
along lines differing from those of the ordinary 
reciprocating engine. The bearing proper is a gun 
metal sleeve that is prevented from turning by a loose- 
fitting dowel. Outside of this sleeve are three con- 
centric tubes having a small clearance between them. 
This clearance is kept constantly filled with oil sup- 



366 ENGINEERING 

plied under light pressure, which permits a vibration 
of the inner shell or sleeve and at the same time tends 
to restrain or cushion it. This arrangement allows the 
shaft to revolve about its axis of gravity, instead of 
the geometrical axis, as would be the case if the bear- 
ing were of the ordinary construction. The journal is 
thus to a certain degree a floating journal, free to run 
slightly eccentric according as the shaft may happen 
to be out of balance. 

A flexible coupling is provided, by means of which 
the power of the turbine is transmitted to the dynamo 
or other machine it is intended to run. The oil from 
all the bearings drains back into a reservoir, and from 
there it is forced up into a chamber, where it forms a 
static head, which gives a constant pressure of oil on 
all the bearings. A secondary valve is located at Vs, 
by means of which high pressure steam may be admitted 
to the steam space E on the same principle that 
high pressure steam is admitted to the low pressure 
cylinder of a compound engine. This valve opens 
automatically in cases of emergency, such as overload, 
failure of the condenser to work, etc. 

The shaft, where it passes through either cylinder 
head, is packed with a water seal packing, consisting 
of a small paddle wheel attached to the shaft, which, 
through centrifugal action, maintains a static pressure 
of about 5 lbs. per sq. in. in the water seal, thus pre- 
venting all leakage while at the same time it is 
frictionless. 

The speed of the Westinghouse-Parsons turbine is 
regulated by a fly ball governor constructed in such 
manner that a very slight movement of the balls 
serves to produce the required change in the supply of 
steam. Fig. 133 is a diagram of the governor 



THE WESTINGHOUSE-PARSONS STEAM TURBINE 367 

mechanism. The ball levers swing on knife edges 
instead of pins. The governor works both ways, that 
is to say, when the levers are oscillating about their 
mid position a head of steam corresponding to full 
load is being admitted to the turbine, and a move- 
ment from this point, either up or down, tends to 
increase or to decrease the supply of steam. 

Referring to Fig. 133, B is a piston directly con- 




FIGURE 133. 



nected to the admission valve. Steam is admitted to 
this piston under control of the pilot valve A, which 
has a slight but continuous reciprocating motion 
derived from the eccentric rod C, and the function of 
the governor is-to vary the plane of oscillation of this 
valve, thus causing it to admit more or less steam to 
piston B. The admission valve, being actuated 
exclusively by piston B, is thus caused to remain open 
for a longer or shorter period of time, according to the 
load upon the turbine. 



368 ENGINEERING 

The vibrations of the admission valve, although very 
slight, are continuous and regular, about 165 per 
minute, and are transmitted primarily by means of an 
eccentric, the rod of which is shown at C, Fig. 133. 

The governor sleeve is used as a floating fulcrum, and 
the points D and E are fixed. By means of this very 
ingenious device the steam is admitted to the turbine in 
puffs, either long or short, according to the demand for 
steam. At full load the puffs merge into an almost con- 
tinuous blast. When the load has increased to the point 
where the valve is wide open continuously, a full head of 
steam is being admitted. Beyond this the secondary 
valve comes into action, thus keeping the speed up to 
normal. 

The rotor requires perfect balancing to insure quiet 
running, but this is easily accomplished in the shop by 
means of a balancing machine used by the builders. 

Steam turbines generally show higher efficiency in 
the use of steam than reciprocating engines do, and 
this fact is due to three leading causes. First, it is 
possible with the turbine to use highly superheated 
steam which, owing to the difficulties attending 
lubrication, could not be used in the reciprocating 
engine. Second, a larger proportion of the heat con- 
tained in the steam is converted into work, for the 
reason that the steam is allowed to expand to a much 
lower pressure and into a higher vacuum. In addition 
to this, the velocity of the expanding steam is utilized 
in a much higher degree in the turbine as compared 
with the reciprocating engine. Third, mechanical fric- 
tion or lost work is reduced to the minimum. Under 
test a 400 K. W. Westinghouse-Parsons steam turbine, 
using steam at 150 lbs. initial pressure and superheated 
about 180 , consumed 11. 17 lbs. of steam per Brake 



THE WESTINGHOUSE-PARSONS STEAM TURBINE 369 

horse power hour at full load. The speed was 
3,550 R. P. M. and the vacuum was 28 in. With 
dry saturated steam the consumption was 13.5 lbs. 
per B. H. P. hour at full load, and 15.5 lbs. at one-half 
load. 

A 1,000 K. W. machine, using steam of 150 lbs. 
pressure and superheated 140 , exhausting into a 
vacuum of 28 in., showed the very remarkable economy 
of 12.66 lbs. of steam per E. H. P. per hour. 

A 1,500 K. W. Westinghouse-Parsons turbine, using 
dry saturated steam of 150 lbs. pressure with 27 in. 
vacuum, consumed 14.8 lbs. steam per E. H. P. hour 
at full load, and 17.2 lbs. at one-half load. 



CHAPTER V 

THE CURTIS STEAM TURBINE 

The Curtis turbine an impulse and reaction machine — Admission 
of the steam — System of expanding nozzles — Ratio of expan- 
sion in four stage machine — Step bearing — Method of lubri- 
cation — Action of the steam in a two stage machine — Static 
force, and force of velocity compared — Speed regulation in 
Curtis turbine — Accomplished in first group of nozzles — How- 
admission of steam is controlled — Velocity of the steam is 
constant, with light or full load — Two main sources of econ- 
omy in the steam turbine — Efficiency tests of Curtis turbine. 

In the Curtis turbine the heat energy in the steam is 
imparted to the wheel, both by impulse and reaction, 
but the method of admission differs from that of the 
Westinghouse-Parsons in that the steam is admitted 
through expanding nozzles in which nearly all of the 
expansive force of the steam is transformed into the 
force of velocity. The steam is caused to pass through 
one, two, or more stages of moving elements, each 
stage having its own set of expanding nozzles, each 
succeeding set of nozzles being greater in number and 
of larger area than the preceding set. The ratio of 
expansion within these nozzles depends upon the 
number of stages, as, for instance, in a two-stage 
machine the steam enters the initial set of nozzles at 
boiler pressure, say 180 lbs. It leaves these nozzles 
and enters the first set of moving blades at a pressure 
of about 15 lbs., from which it further expands to 
atmospheric pressure in passing through the wheels 
and intermediates. From the pressure in the first 
stage the steam again expands through the larger area 
370 



THE CURTIS STEAM TURBINE 371 

of 'the second stage nozzles to a pressure slightly 
greater than the condenser vacuum at the entrance to 
the second set of moving blades, against which it now 
impinges and passes through still doing work, due to 
velocity and mass. 

From this stage the steam passes to the condenser. 
If the turbine is a four-stage machine and the initial 
pressure is 180 lbs., the pressure at the different stages 
would be distributed in about the following manner: 
Initial pressure, 180 lbs.; first stage, 50 lbs.; second 
stage, 5 lbs.; third stage, partial vacuum, and fourth 
stage, condenser vacuum. 

The Curtis turbine is built by the General Electric 
Co. at their works in Schenectady, New York, and 
Lynn, Mass. The larger sizes are of the vertical type, 
and those of small capacity are horizontal. 

Fig. 134 gives a general view of a 5,000 K. W. 
turbine and generator. The generator is shown at the 
top, while the turbine occupies the middle and lower 
section. A portion of the inlet steam pipe is shown, 
ending in one nozzle group at the side. There are 
three groups of initial nozzles, two of which are not 
shown. The revolving parts of this unit are set upon 
a vertical shaft, the diameter of the shaft correspond- 
ing to the size of the unit. For a machine having the 
capacity of the one illustrated by Fig. 134 the diameter 
of the shaft is 14 in. 

The shaft is supported by and runs upon a step 
bearing at the bottom. This step bearing consists of 
two cylindrical cast iron plates, bearing upon each 
other and having a central recess between them into 
which lubricating oil is forced under pressure by a 
steam or electrically driven pump, the oil passing up 
from beneath. A weighted accumulator is sometimes 



372 



ENGINEERING 



installed in connection with the oil pipe as a con- 
venient device for governing the step bearing pumps, 
and also as a safety device in case* the pumps should 
fail, but it is seldom required for the latter purpose, as 




FIGURE 134. 

5,000 K.W. CURTIS STEAM TURBINE DIRECT CONNECTED TO 5,000 

K.W. THREE-PHASE ALTERNATING CURRENT GENERATOR. 



the step bearing pumps have proven, after a long 
service in a number of cases, to be reliable. The 
vertical shaft is also held in place and kept steady by 
three sleeve bearings, one just above the step, one 
between the turbine and generator, and the other near 



THE CURTIS STEAM TURBINE 



373 



the top. These guide bearings are lubricated by a 
standard gravity feed system. It is apparent that the 
amount of friction in the machine is very small, and 
as there is no end thrust caused by the action of the 
steam, the relation between the revolving and station- 
ary blades may be maintained accurately. As a con- 




FIGURE 135. 

500 K.W. CURTIS STEAM TURBINE IN COURSE OF CONSTRUCTION. 

sequence, therefore, the clearances are reduced to the 
minimum. 

The Curtis turbine is divided into two or more stages, 
and each stage has one, two or more sets of revolving 
blades bolted upon the peripheries of wheels keyed to 
the shaft. There are also the corresponding sets of 
stationary blades, bolted to the inner walls of the 
cylinder or casing. As in the Westinghouse-Parsons 



374 ENGINEERING 

type, the function of the stationary blades is to give 
direction to the flow of steam. 

Fig. 135 illustrates one stage of a 500 K. W. turbine 
in course of construction. It will be observed that 
there are three wheels, and that in the spaces between 
these wheels the stationary buckets or vanes are 




REVOLVING BUCKETS FOR CURTIS STEAM TURBINE. 




STATIONARY BUCKETS FOR CURTIS STEAM TURBINE. 
FIGURE 136. 

placed, being firmly bolted to the casing. Fig. 136 
shows sections of both revolving and stationary 
buckets ready to be placed in position. The illustration 
in Fig. 135 shows the lower or last stage. The clear- 
ance between the revolving and stationary blades is 
from 3V to T V in., thus reducing the wastage of steam 
to a very low percentage. The diameters of the 



THE CURTIS STEAM TURBINE 375 

wheels vary according to the size of the turbine, that 
of a 5,000 K. W. machine being 13 ft. 

Fig. 137 shows a nozzle diaphragm with its various 
openings, and it will be noted that the nozzles are set 
at an angle to the plane of revolution of the wheel. 

Fig. 138 is a diagram of the nozzles, moving blades 
ancf stationary blades of a two-stage Curtis steam 
turbine. The steam enters the nozzle openings at the 
top, controlled by the valves shown, the regulation of 
which will be explained later on. In the cut Fig. 138 
two of the valves are open, and the course of the 
steam through the first stage is indicated by the arrows. 




FIGURE 137. NOZZLE. 

After passing successively through the different sets cf 
moving blades and stationary blades in the first stage, 
the steam passes into the second steam chest. The 
flow of steam from this chamber to the second stage 
of buckets is also controlled by valves, but the function 
of these valves is not in the line of speed regulation 
but for the purpose of limiting the pressure in the stage 
chambers, in a manner somewhat similar to the control 
of the receiver pressure in a two-cylinder or three- 
cylinder compound reciprocating engine. 

The valves controlling the admission of steam to the 
second and later stages differ from those in the first 
group in that they partake more of the nature of slide 



376 



ENGINEERING 



valves and may be operated either by hand or auto- 
matically; in fact, they require but very little regulation, 



St:<sorT-> er/nest. 







i<«««««««(a 

~mm~ ~ 



/\Sfovt'r->sr £9 /oc/e-S 



Ato22fe Z7/<pjo/^mo'gr/- 1 




Afovrrt^ jB/QOfiss 



cccccccccccccccccccccc 



/V7ov/r>gr /3/ocfes 



I(<««<« «(««(«««« 



Afo v/ir>jp/3/&afG 3 



III I I.J 



FIGURE 138. 
DIAGRAM OF NOZZLES AND BUCKETS IN CURTIS STEAM TURBINE. 

as the governing is always done by the live steam 
admission valves. 
Action of the Steam in a Two-stage Machine. As 

previously stated, the steam first strikes the moving 
blades in the first stage of a two-stage machine at a 



THE CURTIS STEAM TURBINE 377 

pressure of about 15 lbs. above atmospheric pressure, 
but with great velocity. From this wheel it passes to 
the set of stationary blades between it and the next 
lower wheel. These stationary blades change the 
direction of flow of the steam and cause it to impinge 
the buckets of the second wheel at the proper angle. 

This cycle is repeated Until the steam passes from 
the first stage into the receiving chamber or steam 
chest for the second stage. Its passage from this 
chamber into the second stage is controlled by valves, 
which, as before stated, are regulated either by hand 
or automatically. The course of the steam through 
the nozzles and blades of the second stage is clearly 
indicated by the arrows, and it will be noted that 
steam is passing through all the nozzles. 

At this point it might be well to consider the ques- 
tion which no doubt arises in the mind of the student 
in his efforts to grasp the underlying principles in the . 
action of the steam turbine. Why is it that the 
impingement of the steam, at so low a pressure, against 
the blades or buckets of the turbine, imparts such a 
large amount of energy to the shaft? 

The answer is, because of velocity, and a good 
example of the manner in which velocity may be 
made to increase the capacity of an agent to do work 
is illustrated in the following way: Suppose that a 
man is standing within arm's length of a heavy plate 
glass window and that he holds in his hand an iron 
ball weighing 10 lbs. Suppose the man should place 
the ball against the glass and press the same there with' 
all the energy he is capable of exerting. He would 
make very little, if any, impression upon the glass. 
But suppose that he should walk away from the 
window a distance of 20 ft. and then exert the same 



378 ENGINEERING 

amount of energy in throwing the ball against the 
glass, a different result would ensue. The velocity 
with which the ball would impinge the surface of the 
glass would no doubt ruin the window. Now, not- 
withstanding the fact that weight, energy and time 
involved were exactly the same in both instances, yet 
a much larger amount of work was performed in the 
latter case, owing to the added force imparted to the 
ball by the velocity with which it impinged against 
the glass. 

Speed Regulation. The governing of speed is 
accomplished in the first set of nozzles, and the control 
of the admission valves here is effected by means of 
a centrifugal governor attached to the top end of the 
shaft. This governor, by a very slight movement, 
imparts motion to levers, which in turn work the valve 
mechanism. The admission of steam to the nozzles 
is controlled by piston valves, which are actuated by 
steam from small pilot valves which are in turn under 
the control of the governor. Fig. 139 shows the form 
of governor for a 5,000 K. W. turbine, and Fig. 140 
shows the electrically operated admission valves for 
one set of nozzles. 

Speed regulation is effected by varying the number 
of nozzles in flow, that is, for light loads fewer nozzles 
are open and a smaller volume of steam is admitted to 
the turbine wheel, but the steam that is admitted 
impinges the moving blades with the same velocity 
always, no matter whether the volume be large or 
small. With a full load and all the nozzle sections in 
flow, the steam passes to the wheel in a broad belt and 
steady flow. 

The Curtis Steam Turbine is the result of the investi- 
gations and experiments of Mr. C. G. Curtis of New 



THE CURTIS STEAM TURBINE 



370 



York, and while retaining the advantage of the expand- 
ing nozzle of De La\ r al, it at the same time utilizes the 
energy acquired by velocity, by causing the steam to 




FIGURE 139. GOVERNOR FOR 5,000 K.W. TURBINE. 

impinge the moving buckets of two or more wheels in 
succession. A portion of this velocity force is given 
up in the first stage, and another portion in the second 
stage, and this process is repeated, the steam in each 



380 



ENGINEERING 



case being first caused to expand in divergent nozzles 
and thus acquire new velocity before it is allowed to 
impinge the moving blades of the next lower stage. The 
pressure in each succeeding stage of expansion becomes 
lower and lower, until finally vacuum is reached. 

As previously stated, two of the main sources of 
economy that the steam turbine possesses in a much 
higher degree than does the reciprocating engine are: 

first, its adaptability 
for using super- 
heated steam, and 
second, the possibil- 
ity of maintaining a 
higher degree of 
vacuum. 

k The efficiency 

I 

I shown by the steam 

HH 1 turbine is certainly 

^ mx ^"- - ■ ' ; remarkable, and one 

\ .jr peculiar feature re- 

^**— _ — _——*_- ' garding the machine 

is, that its efficiency 
is not affected by 
variations in load to the same degree as is the efficiency 
of the reciprocating engine. 

A 600 K W. Curtis turbine operating at 1,500 
R P. M., with steam at 140 lbs. gauge pressure and 
28.5 in. vacuum, showed a steam consumption as fol- 
lows, steam superheated 150 : 

At full load, 12.5 lbs. per E. H. P. per hour.. 
At half load, 13.25 lbs. per E. H. P. per hour. 
At one-sixth load, 16.2 lbs. per E. H. P. per hour. 
And at one-third overload, 12.4 lbs. per E. H. P. per 
hour. 




FIGURE 140. ELECTRICALLY OPER- 
ATED VALVE. 



THE CURTIS STEAM TURBINE 381 

This would seem to indicate that the efficiency of 
the steam turbine increases with overload, at least up 
to a certain point. 

In another test of a Curtis turbine, using dry 
saturated steam of 145 lbs. gauge pressure, the steam 
consumption at full load was 14.76 lbs. per E. H. P. 
hour, and at half load the rate was 15.95 lbs. per 
E. H. P. hour. The same machine using steam super- 
heated 150 showed a steam consumption of 
13.27 lbs. per E. H. P.hour, at full load. 

A Curtis turbine carrying a commercial load on a 15- 
hour run showed an average coal consumption as 
follows; the turbine was operated with one boiler 
independently of the other boilers in the battery, and 
the steam was not superheated: Coal consumed per 
E. H. P. hour, 1.86 lbs. 

The highest type of modern reciprocating engine, 
triple expansion, condensing, having steam jacketed 
cylinders, shows a coal consumption of 1.5 to 2 lbs. per 
H. P. per hour, assuming the evaporation to be 8 lbs. 
water per pound of coal. 



CHAPTER VI 

THE HAMILTON-HOLZWARTH STEAM TURBINE 

The Hamilton-Holzwarth steam turbine — Points of difference 
between it and the Westinghouse- Parsons — Small clearances 
necessary — Stationary discs and guide vanes — Running 
wheels— Expansion of the steam and where it occurs — Action 
of the steam within the machine — Various stages in high and 
low pressure casings — Curvature of vanes — Purpose of sta- 
tionary discs — Thrust ball bearings — Description of the gov- 
ernor and regulating mechanism — Close regulation — Method 
of changing speed while running. 

This turbine resembles the Westinghouse-Parsons 
turbine in some respects, prominent of which is that 
it is a full stroke turbine, that is, that the steam flows 
through it in one continuous belt or veil in screw line, 
the general direction being parallel with the shaft. 
But, unlike the Parsons type, the steam in the Hamil- 
ton-Holzwarth turbine is made to do its work only by 
impulse, and not by impulse and reaction combined. 
It might thus be termed an action turbine. 

The Hamilton-Holzwarth steam turbine is based 
upon and has been developed from the designs of Prof. 
Rateau, and is being manufactured in this country by 
the Hooven-Owens-Rentschler Co. of Hamilton, Ohio. 
It is horizontal and placed upon a rigid bed plate 
of the box pattern. All steam, oil and water pipes 
are within and beneath this bed plate, as are also 
the steam inlet valve and the regulating and by-pass 
valves. 

The smaller sizes of this turbine are built in a single 
casing or cylinder, but for units of 750 kilowatts and 
382 



THE HAMILTON-HOLZWARTH STEAM TURBINE 383 

larger the revolving element is divided into two parts, 
high and low pressure. 

There are no balancing pistons in this machine, the 
axial thrust of the shaft being taken up by a thrust 
ball-bearing. The interior of the cylinder is divided 
into a series of stages by stationary discs which are set 
in grooves in the cylinder and are bored in the center 
to allow the shaft, or rather the hubs of the running 
wheels that are keyed to the shaft, to revolve in this 
bore. 

The clearance allowed is as small as practical, as it 
is in this clearance between the revolving hub and the 
circumference of the bore of the stationary disc that 
the leakage losses occur. It should be noted that 
between each two stationary discs there is located a 
running wheel, and that the clearance between the run- 
ning vanes and the stationary vanes is made as slight 
as is consistent with safe practice; otherwise leakage 
would occur here also, and besides this there would be 
a distortion of the steam jet and entrainment of the 
surrounding atmosphere, resulting in a rapid decline in 
economy if the clearance between the stationary and 
moving elements was not reduced to as small a fraction 
as possible. 

As before stated, the stationary discs are firmly 
secured to the interior walls of the casing. At intervals 
on the outside periphery of these discs are located the 
stationary or guide vanes. These are made of drop 
forged steel. They are set in a groove on the outside 
edge of the disc and fastened with rivets. Both disc 
and vanes are then ground, giving the vanes the profile 
that they should have for the most efficient expansion 
of the steam. After this is done a steel ring is shrunk 
on the outside periphery of the vanes and the steam 



384 ENGINEERING 

channels in the disc. These discs are then placed in 
the grooves in the casing at regular intervals, and in 
the spaces between them are the running wheels. 

The casing is divided into an upper and lower half. 
The running wheels are built with a cast steel hub 
having a steel disc riveted on to each side, thus forming 
a circumferential ring space into which the running 
vanes are riveted. A thin steel band or rim is tied on 
the outer edge of the vanes, thus forming an outer wall 
to the steam channels and confining the steam within 
the vanes. These vanes are also milled on both edges, 
on the influx and efflux side of the wheel, thus forming 
them to the shape corresponding to the theoretical 
diagram. 

The running vanes conform in section somewhat to 
the Parsons type, but the action of the steam upon 
them and also within the stationary vanes is different. 
The expansion of the steam and consequent develop- 
ment of velocity takes place entirely within the station- 
ary vanes, which also change the direction of flow of 
the steam and distribute it in the proper manner to the 
vanes of the running wheels, which, according to the 
claims of the makers, the steam enters and leaves at 
the same pressure, thus allowing the wheel to revolve 
in a uniform pressure. 

Fig. 141 shows a general view of the Hamilton- 
Holzwarth turbine, and the action of the steam within 
the machine may be described as follows: After leaving 
the steam separator that is located beneath the bed 
plate, the steam passes through the inlet or throttle 
valve, the stem of which extends up through the floor 
near the high pressure casing and is protected by a 
floor stand and equipped with a hand wheel, shown in 
Fig. 141. The steam now passes through the regulat- 



THE HAMILTON-HOLZWAKTH STEAM TURBINE 



385 



ing valve, which will be described later on. From this 
valve it is led through a curved pipe to the front head 

of the high pressure cas- 
ing or cylinder. In this 
head is a ring channel 
into which the steam 
enters, and from whence 
it flows through the first 
set of stationary vanes. 
In these vanes the first 
stageof expansionoccurs, 
the velocity of the flow 
is accelerated, and the 
direction of flow is 
. changed by the curve of 
2J the vanes in such man- 
§ ner that the steam im- 
o pinges the vanes of the 
fe first running wheel at the 
proper angle and in a full 
cylindrical belt, impart- 
ing by impulse a portion 
of its energy to the wheel. 
Passing through the 
vanes of this wheel, the 
steam immediately enters 
the vanes of the second 
stationary disc, which are 
larger in area than those 
of the first, and here 
occurs the second stage 
of expansion, another acceleration of velocity, and also 
the proper change in direction, and the steam leaves 
this distributer and impinges the vanes of the second 




386 ENGINEERING 

running wheel. This cycle is repeated throughout the 
several stages of the turbine, a certain percentage of 
the heat energy in the steam being imparted by impulse 
to each wheel and thence to the turbine shaft. From 
the last running wheel the steam is led through re- 
ceiver pipes to the front head of the low-pressure 
cylinder, or, if there is but one cylinder, directly to 
the condenser or the atmosphere. 

In the low-pressure casing, which is larger in diam- 
eter than the high-pressure the steam is distributed in 
the same manner as it is in the high-pressure casing. 
There is, however, in the front head of the low-pres- 
sure casing an additional nozzle through which live 
steam may be admitted in case of overload. The 
design of this nozzle is such that the live steam entering 
and passing through it and controlled by the governor 
exerts no back pressure on the steam coming from the 
receiver, but, on the contrary, its action is similar to 
the action of an injector, that is, it tends to suck the 
low-pressure steam through the first set of stationary 
vanes of the low-pressure turbine. 

The first stationary disc of the low-pressure turbine 
has guide vanes all around its circumference, so that 
the steam enters the turbine in a full cylindrical belt, 
interrupted only by the guide vanes. To provide for 
the increasing volume as the steam expands in its 
course through the turbine, the areas of the passages 
through the distributers and running vanes must be 
progressively enlarged. The gradual increase in the 
dimensions of the stationary vanes permits the steam 
to expand within them, thus tending to maintain its 
velocity, while at the same time the vanes guide the 
steam under such a small angle that the force with 
which it impinges the vanes of the next running wheel 



THE HAMILTON-HOLZWARTH STEAM TURBINE 387 

is as effective as possible. The curvature of the vanes 
is such that the steam while passing through them will 
increase its velocity in a ratio corresponding to its 
operation. 

The purpose of the stationary discs is, as has been 
stated, to distribute the steam to the running wheels. 
They also take the back pressure of the steam as it 
impinges the vanes of the running wheels, thus in a 
sense acting as balancing pistons. 

In all 'steam turbines one of the main requisites for a 
quiet-running machine is that the revolving element 
or rotor shall be perfectly balanced. The rotary body 
of the Hamilton-Holzwarth turbine consists of a plu- 
rality of running wheels, each one of which is balanced 
by itself before being placed upon the shaft. All the 
bearings are lubricated in a thorough manner by oil 
forced up into the bottom bushing or shell under slight 
pressure. Flexible couplings are used between the 
high and low-pressure shafts, and for connecting the 
turbine shaft to the generator shaft or other shaft to be 
driven. By means of the thrust ball-bearing on the 
exhaust end of the turbine the shaft may be adjusted 
in an axial direction in such manner as to accurately 
preserve the desired position of the running wheels 
with relation to the stationary discs. 

The governor is of the spring and weight type, 
adapted to high speed, and is designed especially for 
turbine governing. It is directly driven by the turbine 
shaft, revolving with the same angular velocity. Its 
action is as follows: Two discs keyed to the shaft 
drive, by means of rollers, two weights sliding along a 
cross bar placed at right angles through the shaft and 
compressing two springs against two nuts on the cross 
bar. Every movement of the weights, caused by 



388 ENGINEERING 

increasing or decreasing the angular velocity of the 
turbine shaft, is transmitted by means of levers to 
a sleeve which actuates the regulating mechanism. 
These levers are balanced so that no back pressure is 
exerted upon the weights. The whole governor is 
closed in by the discs, one on each side, and a steel 
ring secured by concentric recesses to the discs. In 
order to decrease the friction within the governor and 
regulating mechanism, thrust ball-bearings and friction- 
less roller-bearings are used. 

As previously stated, the regulating valve is located 
beneath the bed plate. One side of it is connected by 
a curved pipe with the front head of the high-pressure 
cylinder and the other side is connected with the inlet 
valve. The regulating valve is of the double-seated 
poppet valve type. Valves and valve seats are made 
of tough cast steel, to avoid corrosion as much as 
possible, and the valve body is made of cast iron. 

Immediately below the regulating valve and forming 
a part of it in one steam chamber is located the by- 
pass regulating valve. Thus the use of a . second 
stuffing box for the stem of this valve is avoided. 
The function of this valve is to control the volume of 
the live steam supply that flows directly to the by-pass 
nozzles in the front head of the low-pressure casing. 
This valve is also a double-seated poppet valve. 

The main regulating valve is not actuated directly by 
the governor, but by means of the regulating mechan- 
ism. The construction and operation of this regulat- 
ing mechanism is as follows: The stem of the 
regulating valve is driven by means of bevel gears by 
a shaft that is supported in frictionless roller-bearings.. 
On this shaft there is a friction wheel that the governor 
can slide across the face of a continuously revolving 



THE HAMILTON-HOLZWARTH STEAM TURBINE 389 

friction disc by means of its sleeve and bell crank 
lever. This revolving disc is keyed to a solid shaft 
which is driven by a coupling frorn a hollow shaft. 
This hollow shaft is driven by the turbine shaft through 
the medium of a worm gear. The solid shaft, with the 
continuously revolving friction disc, can be slightly 
shifted by the governor sleeve so that the two friction 
discs come into contact when the sleeve moves, that 
is, when the angular velocity changes. If this change 
is relatively great, the sleeve will draw the periodically 
revolving friction disc far from the center of the always 
revolving one, and this disc will quickly drive the 
stem of the regulating valve and the -flow of steam will 
thus be regulated. As soon as the angular velocity 
falls below a certain percentage of the normal speed, 
the driving friction disc is drawn back by the governor, 
the regulating valve remains open and the whole regu- 
lating mechanism rests or stops, although the shaft is 
still running. 

Should the angular velocity of the shaft reach a point 
2.5 per cent higher than normal, the governor will shut 
down the turbine. If an accident should happen to 
the governor, due to imperfect material or breaking or 
weakening of the springs, the result would be a shut- 
down of the turbine. 

In order to change the speed of the turbine while 
running, which might be necessary in order to run the 
machine parallel with another prime mover, a spring 
balance is provided, attached to the bell crank lever 
of the regulating mechanism. The hand wheel of this 
spring balance is outside of the pedestal for regulating 
mechanism and near the floor-stand and hand wheel. 
With this spring balance the speed of the turbine may 
be changed 5 per cent either way from normal. 



390 ENGINEERING 

All the bearings of the unit are thoroughly lubricated 
with oil forced under pressure by the oil pump driven 
by means of worm-gearing by the turbine itself. After 
flowing through the bearings the oil is passed through 
a filter and from thence to the oil tank located within 
the bed plate, from whence it is taken by the oil pump. 
All revolving parts are enclosed, and the principal 
part of the regulating mechanism operates in a bath 
of oil. 



CHAPTER VII 

DE LAVAL STEAM TURBINE 

De Laval steam turbine — High velocity — The De Laval divergent 
nozzle — Adiabatic expansion of steam within nozzle — Conver- 
sion of static energy into kinetic — Form of De Laval wheel — 
Speed of buckets — Speed of turbine shaft, and how it is 
reduced — Construction of the wheel — Number of buckets 
required — Number of nozzles — Gear and flexible shaft — 
Description of governor — Vacuum valve — Operation of gov- 
ernor — Efficiency tests — Steam consumption— Cross section 
of wheel showing correct design — Table of sizes, giving speed 
and weight. 

The De Laval steam turbine, the invention of Carl 
De Laval of Sweden, is noted for the simplicity of its 
construction and the high speed of the wheel —10,000 
to 30,000 R. P. M. The difficulties attending such 
high velocities are, however, overcome by the long, 
flexible shaft and the ball and socket type of bearings, 
which allow of a slight flexure of the shaft in order 
that the wheel may revolve about its center of gravity, 
rather than the geometrical center or center of position. 
All high speed parts of the machine are made of forged 
nickel steel of great tensile strength. But one of the 
most striking features of this turbine is the diverging 
nozzle, also the invention of De Laval. 

It is well known that in a correctly designed nozzle 
the adiabatic expansion of the steam from maximum 
to minimum pressure will convert the entire static 
energy of the steam into kinetic. Theoretically this is 
what occurs in the De Laval nozzle. The expanding 
steam acquires great velocity, and the energy of the jet 
391 



ENGINEERING 



of steam issuing from the nozzle is equal to the amount 
of energy that would be developed if an equal volume 
of steam were allowed to adiabatically expand behind 
the piston of a reciprocating engine, a condition, how- 




ever, which for obvious reasons has never yet been 
attained in practice with the reciprocating engine. 
But with the divergent nozzle the conditions are 
different. 

Referring to Fig. 142, a continuous volume of steam 



DE LAVAL STEAM TURBINE 



393 



at maximum pressure is entering the nozzle at E, and, 
passing through it, expands to minimum pressure at F, 
the temperature of the nozzle being at the same time 
constant and equal to the temperature of the passing 
steam. The principles of the De Laval expanding 
nozzle are in fact more or less prominent in all steam 




FIGURE 143. THE DE LAVAL TURBINE WHEEL AND NOZZLES. 



turbines. The facilities for converting heat into work 
are increased by its use, and the losses by radiation 
and cooling influences are greatly lessened. 

The De Laval steam turbine is termed by its builders 
a high-speed rotary steam engine. It has but a single 
wheel, fitted with vanes or buckets of such curvature as 



394 



ENGINEERING 



has been found to be best adapted for receiving the 
impulse of the steam jet. There are no stationary or 




guide blades, the augular position of the nozzles giving 
direction to the jet. Fig. 143 shows the form of wheel 



DE LAVAL STEAM TURBINE 395 

and the nozzles. The nozzles are placed at an angle of 
20° to the plane of motion of the buckets, and the 
course of the steam is shown by the illustration. 

The heat energy in the steam is practically devoted 
to the production of velocity in the expanding 01 
divergent nozzle, and the velocity thus attained by the 
issuing jet of steam is about 4,000 ft. per second. To 
attain the maximum of efficiency the buckets attached 
to the periphery of the wheel against which this jet 
impinges should have a speed of about 1,900 ft. per 
second, but, owing to the difficulty of producing a 
material for the wheel strong enough to withstand the 
strains induced by such a high speed, it has been found 
necessary to limit the peripheral speed to 1,200 or 
1,300 ft. per second. 

Fig. 144 shows a De Laval steam turbine motor of 
300 H. P., which is the largest size built up to the 
present time, its use having been confined chiefly to 
light work. 

The turbine illustrated in Fig. 144 is shown directly 
connected to a 200 fe.VV. two-phase alternator. The 
steam and exhaust connections are plainly shown, as 
also the nozzle valves projecting from the turbine 
casing. The speed of the turbine wheel and shaft is 
entirely too high for most practical purposes, and it is 
reduced by a pair of very perfectly cut spiral gears, 
usually made 10 to 1. These gear wheels are made of 
solid cast steel, or of cast iron with steel rims pressed 
on. The teeth in two rows are set at an angle of go° to 
each other. This arrangement insures smooth running 
and at the same time checks any tendency of the shaft 
towards end thrust, thus dispensing ,with a thrust 
bearing. 

The working parts of the machine are clearly illus- 



396 



ENGINEERING 




FIGUKE 145. 



trated in Fig. 145, and a fairly good conception of the 
assembling of the various members, and especially the 
reducing gears, may be had by reference to Fig. 146, 



DE LAVAL STEAM TURBINE 397 

which shows a 110 H. P. turbine and rotary pump with 
the upper half of the gear case and field frame removed 
for purposes of inspection. The slender shaft is seen 
projecting from the center of the turbine case, and upon 
this shaft are shown the small pinions meshing into the 
large spiral gears upon the two pump shafts. 

Referring to Fig. 145, A is the turbine shaft, B is the 
turbine wheel, and C is the pinion. As the turbine 
wheel is by far the most important element, it will be 
taken up first. It is made of forged nickel steel, and 
it is claimed by the builders, the De Laval Steam 
Turbine Co. of Trenton, New Jersey, that it will with- 
stand more than double the normal speed before 
showing any signs of distress. A clear idea of the 
construction of the wheel and buckets may be had by 
reference to Fig. 143. The number of buckets varies 
according to the capacity of the machine. There are 
about 350 buckets on a 300 H. P. wheel. The buckets 
are drop forged and made with a bulb shank fitted in 
slots milled in the rim of the wheel. 

Fig. 147 is a sectional plan of a 30 H. P. turbine con- 
nected to a single dynamo, and Fig. 148 is a sectional 
elevation of the same. 

The steam, after passing the governor valve C, Fig. 
148, enters the steam chamber D, Fig. 147, from 
whence it is distributed to the various nozzles. The 
number of these nozzles depends upon the size of the 
machine, ranging from one to fifteen. They are 
generally fitted with shut-off valves (see Fig. 144) by 
which one or more nozzles can be cut out when the 
load is light. This renders it possible to use steam at 
boiler pressure, no matter how small the volume 
required for the load. This is a matter of great 
importance, especially where the load varies con- 



398 



ENGINEERING 




siderably, as, for instance, there are plants in which 
during certain hours of the day a 300 H. P. machine 
may be taxed to its utmost capacity and during certain 



DE LAVAL STEAM TURBINE 



899 




400 ENGINEERING 

other hours the load on the same machine may drop to 
50 H. P. In such cases the number of nozzles in action 
may be reduced by closing the shut-off valves until the " 
required volume of steam is admitted to the wheel. 
This adds to the economy of the machine. After pass- 
ing through the nozzles, the steam, as elsewhere 
explained, is now completely expanded, and in imping- 
ing on the buckets its kinetic energy is transferred to 
the turbine wheel. Leaving the buckets, the steam 
now passes into the exhaust chamber G, Fig. 147, and 
out through the exhaust opening H, Fig. 148, to the 
condenser or atmosphere as the case may be. 

The gear is mounted and enclosed in the gear case I, 
Fig. 147. J is the pinion made solid with the flexible 
shaft and engaging the gear wheel K. This latter is 
forced upon the shaft L, which, with couplings M, 
connects to the dynamo or is extended for other 
transmission. 

O, Fig. 148, is the governor held with a taper shank 
in the end of the shaft L, and by means of the bell 
crank P operates the governor valve C. The flexible 
shaft is supported in three bearings, Fig, 147. Q and 
R are the pinion bearings and S is the main shaft bear- 
ing which carries the greater part of the weight of the 
wheel. This bearing is self-aligning, being held to its 
seat by the spring and cap shown. 

T, Fig. 147, is the flexible bearing, being entirely 
free to oscillate with the shaft. Its only purpose is to 
prevent the escape of steam when running non-con- 
densing, or the admission of air to the wheel case when 
running condensing. The flexible shaft is made very 
slender, as will be observed by comparing its size with 
that of the rotary pump shaft in Fig. 146. It is by means 
of this slender, flexible shaft that the dangerous feature 



DE LAVAL STEAM TURBINE 



401 




402 



ENGINEERING 



of the enormously high speed of this turbine is 
eliminated. 

The governor is of the centrifugal type, although 
differing greatly in detail from the ordinary fly ball 
governor, as will be seen by reference to Fig. 149. It 
is connected directly to the end of the gear wheel shaft. 
Two weights B are pivoted on knife edges A with 




figure 149. 



hardened pins C, bearing on the spring seat D. E is 
the governor body fitted in the end of the gear wheel 
shaft K and has seats milled for the knife edges A. It 
is afterwards reduced in diameter to pass inside of the 
weights and its outer end is threaded to receive the 
adjusting nut I, by means of which the tension of the 
spring, and through this the speed of the turbine, is 
adjusted. When the speed accelerates, the weights, 



DE LAVAL STEAM TURBINE 403 

affected by centrifugal force, tend to spread apart, and 
pressing on the spring seat at D push the governor pin 
G to the right, thus actuating the bell crank L and 
cutting off a part of the flow of steam. 

It has been found necessary with this turbine, when 
running condensing, to introduce a valve termed a 
vacuum valve, also controlled by the governor, as it has 
been found that the governor valve alone is unable to 
hold the speed of the machine within the desired limit. 
The function of the vacuum valve is as follows: The 
governor pin G actuates the plunger H, which is 
screwed into the bell crank L, but without moving the 
plunger relative to said crank. This is on account of 
the spring M being stirrer than the spring N, whose 
function is to keep the governor valve open and the 
plunger H in contact with the governor pin. When 
a large portion of the load is suddenly thrown off, the 
governor opens, pushing the bell crank in the direction 
of the vacuum valve T. This closes the governor 
valve, which is entirely shut off when the bell crank is 
pushed so far that the screw O barely touches the 
vacuum valve stem J. Should this not check the speed 
sufficiently, the plunger H is pushed forward in the 
now stationary bell crank and the vacuum valve is 
opened, thus allowing the air to rush into the space P 
in which the turbine wheel revolves, and the speed is 
immediately checked. 

The main shaft and dynamo bearings are ring oiling. 
The high-speed bearings on the turbine shaft are fed 
by gravity from an oil reservoir, and the drip oil is 
collected in the base and maybe filtered and used over 
again. 

The fact that the steam is used in but a single stage 
or set of buckets and then allowed to pass into the 



404 



ENGINEERING 



exhaust chamber might appear at first thought to be a 
great loss of kinetic energy, but, as has been previously 
stated, the static energy in the steam as it enters the 
nozzles is converted into kinetic energy by its passage 
through the divergent nozzles, and the result is a 
greatly increased volume of steam leaving the nozzles 
at a tremendous velocity, but at a greatly reduced 




L23 



FIGURE 150. 



pressure — practically exhaust pressure — impinging 
against the buckets of the turbine wheel and thus 
causing it to revolve. 

Efficiency tests of the De Laval turbine show a high 
economy in steam consumption, as, for instance, a test 
made by Messrs. Dean and Main of Boston, Mass, on 
a 300 H P. turbine, using saturated steam at about 
200 lbs. pressure per sq. in. and developing 333 Brake 



DE LAVAL STEAM TURBINE 



405 



H. P., showed a steam consumption of 15.17 lbs. per 
B. H. P., and the same machine, when supplied with 
superheated steam and carrying a load of 352 B. H. P., 
consumed but 13.94 lbs. per B. H. P. These results 
compare most favorably with those of the highest type 
of reciprocating engines. 

Fig. 150 shows a cross section of a 300 H. P. De 
Laval wheel, showing the design necessary for with- 
standing the high centrifugal stress to which these 
wheels are subjected. All De Laval wheels are tested 
to withstand the centrifugal stress of twice their normal 
velocity without showing signs of fatigue. 

The following table gives the sizes and weights of 
some of these turbines, together with revolutions per 
minute of the turbine shaft and the main shaft. 



Horse Power 


Revolutions 
Turbine Shaft 


Revolutions 
Main Shaft 


Approximate 
Weight 
Pounds 


5 

- 10 

20 

75 

110 

225 

300 


30,000 
24,000 
20,000 
16,400 
13,000 
11,060 
10,500 


3,000 
2,400 
2,000 
1,500 
1,200 ■ 
900 
900 


330 

650 

1,250 

5,000 

8,000 

15,000 

20,000 



CHAPTER VIII 

DISPOSAL OF THE EXHAUST STEAM OF STEAM 
TURBINES 

Advantages of exhausting into a condenser — Possible to maintain 
higher vacuum in condenser of a turbine than with reciprocat- 
ing engine — Surface condensers — Bulkley injector condenser 
— Steam turbine condensing apparatus at St. Louis Exposition, 
1904 — Dry air pump — Gain in economy from high vacuum — 
Cost of operating auxiliaries — Necessity of excluding all air 
from condensing system — Ways in which air may be en- 
trained — Comparative efficiency of turbines and reciprocating 
engines — Percentage of saving per each inch increase in 
vacuum above 25 inches — Advantages of superheating the 
steam — Outlook for future of steam turbines. 

As in the case of the reciprocating engine, the 
highest efficiency in the operation of the steam turbine 
is obtained by allowing the exhaust steam to pass into 
a condenser, and experience has demonstrated that it 
is possible to maintain a higher vacuum in the con- 
denser of a turbine than in that of a reciprocating 
engine. This is due, no doubt, to the fact that in the 
turbine the steam is expanded down to a much lower 
pressure than is possible with the reciprocating engine. 

The condensing apparatus used in connection with 
steam turbines may consist of any one of the modern 
improved systems, and as no cylinder oil is used within 
the cylinder of the turbine, the water of condensation 
may be returned to the boilers as feed water. If the 
condensing water is foul or contains matter that would 
be injurious to the boilers, a surface condenser should 
be used. If the water of condensation is not to be used 
406 



DISPOSAL OF THE EXHAUST STEAM 407 

in Hie boilers, the jet system may be employed. 
Another type of condenser that is being successfully 
used with steam turbines is the Bulkley injector 
condenser. 

Among the steam turbines that were on exhibition at 
the St. Louis exposition in 1904 the Westinghouse- 
Parsons and the General Electric Curtis turbines were 
each equipped with Worthington surface condensers, 
fitted with improved auxiliary apparatus consisting of 
dry vacuum pumps, either horizontal of the well-known 
Worthington type, or rotative motor-driven, a hot well 
pump, and a pump for disposing of the condensed 
steam from the exhaust system. The two latter pumps 
were of the Worthington centrifugal type. The 
Hamilton-Holzwarth turbine was equipped with a 
Smith-Vaile surface condenser, fitted with a duplex 
double-acting air pump, a compound condensing 
circulating pump, and a rotative dry vacuum pump, 
motor-driven. The vacuum maintained was high, 28 
to 28.5 in. 

As an instance of the great gain in economy effected 
by the use of the condenser in connection with the 
steam turbine, a 750 K. W. Westinghouse-Parsons 
turbine, using steam of 150 lbs. pressure not super- 
heated and exhausting into a vacuum of 28 in., showed 
a steam consumption of 13.77 l° s - P er B. H. P. per 
hour, while the same machine operating non-condensing 
consumed 28.26 lbs. of steam per B. H. P. hour. 
Practically the same percentage in economy effected by 
condensing the exhaust applies to the other types of 
steam turbines. 

With reference to the relative cost of operating the 
several auxiliaries necessary to a complete condensing 
outfit, the highest authorities on the subject place the 



408 ENGINEERING 

power consumption of these auxiliaries at from 2 to 7 
per cent of the total turbine output of power. A por- 
tion of this is regained by the use of an open heater 
for the feed water, into which the exhaust steam from 
the auxiliaries may pass, thus heating the feed water 
and returning a part of the heat to the boilers. 

A prime requisite to the maintenance of high vacuum, 
with the resultant economy in the operation of the 
condensing apparatus, is that all entrained air must be 
excluded from the condenser. There are various ways 
in which it is possible for air to find its way into the 
condensing system. For instance, there may be an 
improperly packed gland, or there may be slight leaks 
in the piping, or the air may be introduced with the 
condensing water. This air should be removed before 
it reaches the condenser, and it may be accomplished 
by means of the "dry" air pump. 

This dry air pump is different from the ordinary air 
pump that is used in connection with most condensing 
systems. The dry air pump handles no water, the 
cylinder being lubricated with oil in the same manner 
as the steam cylinder. The clearances also are made 
as small as possible. These pumps are built either in 
one or two stages. 

A barometric or a jet condenser may be used, or a 
surface condenser. The latter type lessens the danger 
of entrained air, besides rendering it possible to return 
the condensed steam, which is pure distilled water, to 
the boilers along with the feed water, a thing very much 
to be desired in localities where the water used for feed- 
ing the boilers is impregnated with carbonate of lime 
or other scale-forming ingredients. 

In comparing the efficiency of the reciprocating 
engine and the steam turbine it is not to be inferred 



DISPOSAL OF THE EXHAUST STEAM 400 

that reciprocating engines would not give better results 
at high vacuum than they do at the usual rate of 25 to 
26 in., but to reach and maintain the higher vacuum of 
28 to 28.5 in. with the reciprocating engine would 
necessitate much larger sizes of the low-pressure 
cylinder, as also the valves and exhaust pipes, in order 
to handle the greatly increased volume of steam at the 
low pressure demanded by high vacuum. 

The steam turbine expands its working steam to 
within I in. of the vacuum existing in the condenser, 
that is, if there is a vacuum of 28 in. in the condenser 
there will be 27 in. of vacuum in the exhaust end of 
the turbine cylinder. On the other hand, there is 
usually a difference of 4 or 5 in. (2 to 2.5 lbs.) between 
the mean back pressure in the cylinder of a recipro- 
cating condensing engine and the absolute back pres- 
sure in the condenser. 

It therefore appears that the gain in economy per 
inch increase of vacuum above 25 in. is much larger 
with the turbine than it is with the reciprocating 
engine. Mr. J. R. Bibbins estimates this gain to be 
as follows: between 25 and 28 in. there is a gain of 3^ 
to 4 per cent per inch of increase, and at 28 in. 5 per 
cent. These results have been obtained by means of 
exhaustive tests conducted by Mr. Bibbins. Other 
high authorities on the steam turbine all agree as to the 
great advantages to be derived by incurring the extra 
expense of erecting a condensing plant that is capable 
of maintaining the high vacuum necessary to high 
efficiency. 

Another method by which the steam consumption of 
the turbine may be materially decreased and a great 
gain in economy effected is by superheating the steam. 
The amount of superheat usually specified is ioo°, and 



410 ENGINEERING 

the apparatus employed for producing it maybe easily 
mounted in the path of the waste gases. The steam 
may thus be superheated without extra cost in fuel, and 
an increase of 8 to 10 per cent in economy effected. 
The independent superheater requires extra fuel and 
labor, and the gain in this case is doubtful, but there 
can be no question as to the wisdom of utilizing the 
waste flue gases for superheating the steam. 

As previously stated, the steam turbine is peculiarly 
adapted for the use of highly superheated steam and 
high vacuum, and in these two particulars it excels the 
reciprocating engine At the present time many large 
plants are equipped with turbine engines that are giving 
the best of results, and the outlook for the future 
employment of this type of power producer is certainly 
very promising. 



PART III 
Electricity for Engineers 



Electricity for Engineers 

CHAPTER I 

The Electric Current— The Ampere— The Volt— The Ohm— The 
Watt — Divided Circuits. 

The Electric Current. All electrical phenomena with 
which we have to deal are produced through the 
medium of the electric current. This current flows 
only in a conductor of electricity. Among the most 
noteworthy of the conductors are the various metals; 
the most useful, and in fact the only one in general 
use for light and power purposes, being copper. 

Every conductor offers some resistance to the flow 
of current, just as every pipe offers resistance to the 
flow of steam or water. Just how this resistance varies 
we shall see later on. In order to familiarize ourselves 
with the most important electrical phenomena let us 
consider Fig. I. The current is assumed to leave the 
battery at the +, or positive, pole and flow along the 
wires, etc., to the negative, or - pole, and as it passes 
through the coils of wire wound about the iron bar it 
produces magnetism in the bar. If the bar is of soft 
iron the magnetism lasts only while the current is 
flowing, but a bar of hardened steel will permanently 
retain its magnetism. The current will also heat the 
incandescent lamp until it emits light, and the fine 
wire, R, to the melting point, if desired. In passing 
through the water in the jar, it will decompose it, 
forming oxygen and hydrogen gas. If, instead of 
5 



6 



ELECTRICITY FOR ENGINEERS 



water, the jar is filled with a proper solution, one of 
the copper plates in the solution will be gradually 
eaten away and the other added to. If we now discon- 
nect our wires from the battery and connect I at 2, and 
2 at I, the chemical action in the jar will be reversed, 
the lamp and fine wire, R, will heat as before, no differ- 
ence being noticeable. The iron bar will also be a 
magnet as before, but the end that before attracted 
the north seeking end of a compass needle will now 
reDel it and attract the south seeking end of the same 




figure 1. 



needle. The wire which connects the various devices, 
and the devices themselves, constitutes an electric cir- 
cuit, and the current is said to flow in such a circuit 
along the wire, just as water flows in a pipe. The 
solid lines form what is known as a series circuit, 
while the dotted lines form a multiple circuit. In the 
latter case, each piece of apparatus receives current 
independent of the others. In the series circuit the 
same current passes through all. If the small wire a 
is connected to b, no current will flow through R; it 



ELECTRICITY FOR ENGINEERS 7 

will all flow through a and b. If the wire X be con- 
nected to Y, all current will flow through it and none 
through any other part of the circuit. The current 
obeys the same law as does water; it takes the path 
which offers the least resistance to its flow. 

Such substances as effectually prevent current from 
flowing through them are known as insulators. Some 
of them are 

Dry Air, Mica, 

Glass, Shellac, 

Silk, Oil, 

Asbestos, Paraffine, 

Porcelain, Wool, 

Cotton, Paper, 

Rubber, Gutta Percha, 

and because the following substances have a low resist- 
ance they are known as conductors of electricity. 
Their relative conductivity is in the following order, 
silver being the best: 

Silver, 

Copper, 

Gold, 

Platinum 

Iron, 

Tin, 

Lead, etc. 

The Ampere. The ampere is the unit of volume or rate 
of flow, and in speaking of a flow of so many amperes, 
we mean substantially the same thing, electrically 
speaking, as though we referred to so many gallons of 
water, mechanically speaking. The number of amperes 
flowing over a wire deliver power, much or little, pro- 



8 ELECTRICITY FOR ENGINEERS 

portional to the electromotive force or pressure under 
which they flow; just as the number of gallons of water 
flowing through a pipe toward a water wheel deliver a 
large or small quantity of power to the wheel, propor- 
tional to the pressure under which the water flows. If 
ioo amperes were flowing at a pressure of 10 volts they 
would produce the same power as though there were 
io amperes flowing at ioo volts, exactly as ioo gals, of 
water flowing at a pressure of io lbs. to the square inch 
would produce the same power as io gals, flowing at a 
pressure of ioo lbs. to the square inch. In both cases, 
however, for convenience, we have not considered the 
size of either wire or pipe, but with the wire, as with 
the pipe, as we increase the diameter we decrease the 
friction or resistance. In speaking of the gallon we, 
of course, have something material on which we can 
base the unit gallon. We may take a vessel I ft. wide, 
I ft. long and I ft. high, and this vessel will hold I cu. 
ft. of water. This cubic foot would contain jy^ gals.; 
but in the case of the ampere we must adopt another 
method. We shall take an earthenware tank in which 
is contained a solution of copper sulphate and add one- 
tenth of one per cent, sulphuric acid. We shall next 
take two copper plates and hang them into this solu- 
tion, keeping them spaced one inch apart, vertically. 
Having washed these plates in clear water, rounded off 
the corners and dried them thoroughly, we must next 
weigh them very carefully before submerging them in 
the liquid. We may now connect both plates to a 
source from which we can obtain a -current of electri- 
city and allow the current to flow from one plate to 
another, through the liquid, for a period of time which 
we must measure by a watch or clock. After current 
has flowed for several hours we will remove the plates, 



ELECTRICITY FOR ENGINEERS 1) 

wash them in clean water, and then dip in a bath of 
water containing a very small amount of sulphuric acid 
to prevent oxidization, dry them and carefully weigh 
them again. It will be found that the negative plate 
has increased in weight by what is called electrolytic 
action. Now weigh the negative plate and ascertain 
the exact number of grammes of copper deposited on 
its surface, or, in other words, find how many grammes 
heavier the plate is now than it was before it went into 
the bath. With these data in our possession we will 
multiply the time in seconds that current was passing 
through the plates by .000329 and divide the number 
of grammes deposited on the plate by the result. The 
quotient will be the number of amperes that passed 
from plate to plate. This I give simply to show you 
the manner in w r hich the ampere can be ascertained. 
It is that current which will deposit .000329 gramme 
per second on one of the plates of a voltameter, as 
above described. It is also the current produced by 
one volt acting through a resistance of one ohm. 

In other words, the ampere is that current which 
would be forced over a wire having a resistance of one 
ohm by a pressure of one volt. 

The ampere-hour is the unit of electrical quantity in 
general use. It is the quantity of electricity conveyed 
by one ampere flowing for one hour, or one-half 
ampere flowing for two hours; or again, one-fourth 
ampere flowing for four hours. In each case the sum 
total would be one ampere-hour." It must, however, 
be noted that an ampere-hour with the pressure at no 
volts would deliver just one-half as much power as an 
ampere-hour at 220 volts. 

An ordinary 16 *candle-power no volt incandescent 
lamp requires a current of about one-half an ampere, 



10 ELECTRICITY FOR ENGINEERS 

while a lamp of the same candle-power at 220 volts 
requires but one-fourth of an ampere, and a 52 volt 
lamp about one ampere. 

A milli-ampere is the one-thousandth (yoW) P ai "t °f 
an ampere. 

The Coulomb. The Coulomb is the unit of quantity. 
It is the quantity of current delivered by one ampere 
flowing for one second. 

The Volt. By electromotive force, volts, or potential, 
we mean electrically about the same as we do when 
speaking of pounds pressure as indicated on a steam 
gauge. If we connect a volt-meter between a positive 
and a negative wire we find that it indicates a certain 
number of volts; the volt-meter then indicates electrical 
pressure just as a steam gauge indicates steam pressure. 
The difference in potential or pressure between two 
wires we will assume to be 100 volts, and the difference 
of potential between the inside of a pipe and the atmos- 
phere also at 100 lbs. to the square inch. The steam 
gauge is closed at one end of the tube which operates it, 
and hence, the pressure from the interior of the pipe 
does not flow into the atmosphere; in other words, the 
resistance offered to the pressure prevents the water 
from escaping into the atmosphere. In the case of 
the volt-meter the resistance of the wires used in its 
construction prevents any great quantity of electricity 
from flowing out of the positive wire and into the 
negative through the volt-meter coil. If the gauge 
were accidentally broken off the pipe, the resistance to 
the pressure on the inside of the pipe would be greatly 
lowered and allow the water to flow into the atmos- 
phere. If a piece of ordinary wire were connected to 
the positive and negative wires, where we have just 
connected our volt-meter, it would form a path of such 



ELECTRICITY FOR ENGINEERS 11 

low resistance and allow all the current to flow through 
it, so there would be no pressure indicated in the volt- 
meter. This would "be called a "short circuit." With 
a volt-meter there is always a small amount of current 
flowing from a positive to a negative wire through the 
coil in the meter. This current is neccesary to produce 
the reading on the meter, but we need not consider 
this current at present, the quantity being very small. 

One volt (unit of pressure) will force one ampere 
(unit of current) over one ohm (unit of resistance). 

Potential is a term quite frequently used to express 
the same idea as voltage or electromotive force, but its 
meaning is somewhat different. Suppose that a steam 
engine is working with ioo lbs. of pressure at the 
throttle valve, and exhausting into a heating system or 
system of piping that offers a back pressure of 5 lbs. to 
the square inch; in other words, the resistance to the 
flow of steam out of the exhaust pipes of this engine is 
such that the remaining pressure, when the engine has 
exhausted, is 5 lbs. Now it will readily be seen that 
the total pressure utilized to do the work would be 100 
lbs. less 5 lbs., or 95 lbs., and therefore the potential 
would be 95 lbs. Now, if we are using electricity at 
100 volts pressure, and lose 5 volts in overcoming 
resistance, we have a potential of 95 volts left. When- 
ever work is done by a steam engine a certain amount 
of pressure is lost by condensation, doing work and by 
overcoming friction. This loss may be considered the 
same as a loss of potential, for in the use of electricity 
any loss in pressure of volts that may occur from 
doing work or overcoming resistance is called a loss of 
potential. 

In open arc lamps the loss of potential across the 
terminals or binding posts is about 50 volts; that is, 50 



12 ELECTRICITY FOR ENGINEERS 

volts have been absorbed or used in producing light. 
You can now readily understand that electromotive 
force means force, pressure, energy, and that by 
potential we mean the capacity to do work or the 
effective pressure to do work. While we are speaking 
of electromotive force we may consider some of the 
advantages of high and low electromotive forces. 
High electromotive force, like steam at high pressure, 
is far more economical in transmission or utilization 
because the quantity may be that much smaller. 

When transmitted to great distances, high electro- 
motive forces, like high water or steam pressures, are 
far more desirable on account of the reduction in fric- 
tion losses; but this is partially offset by the necessity 
of using, in water transmission, a much stronger pipe 
for the high pressure than would be necessary for the 
low pressure, and in the transmission of current at a 
high electromotive force or pressure it becomes neces- 
sary to use wires with far better insulating material 
than would be required for the transmission of elec- 
tricity at low pressure. Increasing the pressure or 
electromotive force always means more danger, even if 
you know the pipes are extra strong or the insulation 
of the wire is of unusuallv high resistance; for if any- 
thing should happen the consequences would be far 
more serious with high than with low pressures. But 
notwithstanding all this, engineers are continually 
increasing the pressures of electrical machinery. 

Static electricity is a term applied to electricity pro- 
duced by friction, and a static discharge of electricity 
usually consists of an infinitely small quantity but a 
very high electromotive force or pressure. Discharges 
of lightning are extremely high in voltage, but the 
quantity of current that flows is very small. 



ELECTRICITY FOR ENGINEERS 13 

The Ohm. The ohm is the unit of resistance. Resist- 
ance, electrically speaking, is much the same thing as 
friction in mechanics. If a wire or pipe of a certain 
length is delivering 10 gals, or 10 amperes at a pressure 
of ioo lbs. or ioo volts, and we propose to double the 
flow without increasing the pressure, it will be necessary 
for us to increase the diameter of the pipe and wire in 
order to lower the resistance of the wire and the friction 
of the pipe to one-half of what it was before. If we 
desire the best results from the pipe, we lower its fric- 
tion by reaming out all burrs and avoiding all unneces- 
sary bends and turns; likewise if we desire the best 
results from the wire we will have the copper of which 
it is constructed as nearly pure as possible, and we 
will install the wire where its temperature will not be 
unnecessarily high, avoiding boiler rooms and other 
hot places. Resistance of the wire increases slightly 
with an increase in temperature. 

For every additional degree centigrade the resistance 
of copper wire increases about 0.4 per cent., or for 
every additional degree Fahrenheit about 0.222 per 
cent. Thus a piece of copper wire having a resistance 
of 10 ohms at 32 F. would have a resistance of n.ic 
ohms at 82 F. An annealed wire is also of lower 
resistance than a hard drawn wire of the same size. 
A good idea of the value of an ohm may be had from 
the following table, which gives the length of differ- 
ent wires required to make one ohm resistance. 

FEET PER OHM OF WIRE (B. & S.). 

94 feet of No. 20 605 feet of No. 12 

150 " 18 961 " 10 

239 " 16 1529 " 8 

380 " 14 2432 " 6 

3867 feet of No. 4 



14 ELECTRICITY FOR ENGINEERS 

We have not as yet established a unit of mechanical 
friction, therefore when we speak of mechanical fric- 
tion we refer to it as requiring a certain quantity of 
power to overcome it. When, however, resistance to 
the flow of electricity is spoken of it is referred to as 
so many ohms. It can be measured in Several ways, 
the most reliable and convenient being by an instru- 
ment called the Wheatstone Bridge. It can also be 
calculated if the length and diameter of the wire or 
conductor is known, as will be shown later on. 

The basis of all electrical calculation is Ohm's law. 
This law reads: 

"The strength of a continuous current in a circuit is 
directly proportional to the electromotive force acting 
on that circuit, and inversely proportional to the resist- 
ance of the circuit." In other words, the current is 
equal to the volts divided by the ohms. Expressed in 
symbols, C = E/R; C being current, E voltage, and R 
resistance. If an incandescent lamp having a resist- 
ance of 200 ohms be placed in a socket where the 
pressure is 115 volts, the resulting current through 
such a lamp would be 115 divided by 200, or .575 of an 
ampere. 

From the formula C = E/R, two others are deduced. 
The volts divided by the amperes equal the ohms, 
E/C = R. 

The amperes multiplied by the ohms equal the volts, 
CxR = E. 

The Watt. The watt is the unit of power. It is an 
ampere multiplied by a volt; just as the unit of mechan- 
ical power, called the foot pound, is the result of the 
pound multiplied by the space in feet through which it 
moves. If a current of say 100 amperes, flews over a wire 
at a pressure of 10 volts, the power delivered will equal 



ELECTRICITY FOR ENGINEERS " 15 

ioo amperes x 10 volts = 1,000 watts. If a current of 
io amperes flows over a wire at a pressure of ioo volts, 
the power would be exactly the same, io amperes x ioo 
volts, or 1,000 watts. But, of course, in the first case it 
would require a wire ten times as large to deliver the 
1,000 watts as would be necessary in the latter case. 
If a weight of 10 pounds were being elevated through 
space at the rate of ioo ft. per minute the power 
equivalent would be io lbs. x ioo ft., or 1,000 ft. lbs. 
If an arc lamp consumes 10 amperes at a pressure of 
70 volts, its power consumption is 10 x 70, or 700 watts. 
One watt is the power developed when 44.25 ft. lbs. 
of work are done per minute. Seven hundred forty- 
six' watts equal one horse power. The watt-hour 
is the unit of electric work, and is a term employed to 
indicate the expenditure of one watt for one hour. 
The kilo watt-hour is the term employed to indicate 
the expenditure of an electric power of 1,000 watts for 
one hour. 

The work done per second when a power of one watt 
is being developed is called the joule, and a joule is 
equal to .7375 ft. lbs. 

Electromotive force times current equals watts. 
The square of the current multiplied by the resistance 
equals watts; and the voltage multiplied by itself and 
divided by the resistance equals watts. Expressed in 
symbols, these explanations would look like this: 
W.fExQ. W = C 3 x R. W = E'^R. 

First. If we have an electromotive force or voltage of 
10 volts and a current of 20 amperes, we have 10 x 20 = 
200 watts. 

Second. If we have a current of 10 amperes and a 
resistance of 30 ohms, we would have 10 x 10 x 30 = 3,000 
watts. 



16 ELECTRICITY FOR ENGINEERS 

Third. If we have an electromotive force or voltage 
of 10 volts and a resistance of 20 ohms, we would have 
10 x 10, or 100 ■*■ 20, or 5 watts. 

In the above formulas E stands for voltage, C for 
current, R for resistance and W for watts. 

Divided Circuits. Currents of electricity, although 
they have no such material existence as water or 
steam, still obey the same general law; that is, they 
flow and act along the lines of least resistance. If a 
pipe extending to the top of a ten story building had 
a very large opening at the first floor, it would be im- 
possible to force water to the top floor. All the water 
would run out at the first floor. If the opening at the 
first floor were small only a part of the water would 
escape through it, some would reach the top of the 
building. The flow of water in each case is inversely 
proportional to the resistance offered to it by the dif- 
erent openings. 

The same thing is true of currents of electricity. 
Where several paths are open to a current of electri- 
city the flow through them will be in proportion to 
their conductivities, which is the inverse ratio of their 
resistances. As an illustration, the current flow 
through all of the lamps, Fig. 2, is the same, because 



figure 2. 

each lamp offers the same resistance. But if we 
arrange a number of lamps as in Fig. 3, the lamps in 
series will offer twice as much resistance as the single 



ELECTRICITY FOR ENGINEERS 



17 



A, 



OB 



FIGURE 3. 

lamps, and will receive but half the current of the 
single lamp. In Fig. 4 we have still another arrange- 
ment. The lamp A limits the current which can flow 
through B and C, and that current which does flow 




FIGURE 4. 



divides between B and C in proportion to their con- 
ductivities. If B has a resistance of no ohms and C 
220 ohms, then B will carry two parts of the current 
and C only one. The combined resistance of all 
lamps, Fig. 2, equals the resistance of one lamp 
divided by the number of lamps. The combined resist- 
ance, Fig. 3, equals the sum of the resistances of the 
two lamps at A multiplied by the resistance of B and 
divided by the sum of all the resistances. If the resist- 
ance of each of the lamps were no ohms, the problem 
would work out thus: ^g^ = 73 /s. 

In Fig. 4 the total resistance is |}o+So + 1 10 = l8 3^- 

One practical illustration of the above law may be 

found in the method of switching series arc lamps, 



18 



ELECTRICITY FOR ENGINEERS 



Fig. 5. As long- as the switch S is open the arc lamp 
burns, but as soon as the switch is closed the lamp is 




FIGURE 5. 



extinguished because the resistance of the short wire 
and the switch S is so much less than that of the arc 
lamp that practically all the current flows through S. 



CHAPTER II 

WIRING SYSTEMS — CALCULATION OF WIRES — WIRING 
TABLES. 

Wiring Systems. The system of wiring which is most 
generally used for incandescent lighting and ordinary 
power purposes is called the two wire parallel system. 
In this system of wiring the two wires run side by side, 
one of them being the positive and one the negative. 
The lamps, motors and other devices are then con- 
nected from one wire to the other. A constant pressure 
of electricity is maintained between the two wires, and 
the number and size of lamps, or other apparatus, 
connected to these two wires, determine how many 
amperes are required. Each lamp or motor is inde- 
pendent of the others and may be turned on or off 
without disturbing the others. 

A diagram of such a system is shown in Fig. 6. 




FIGURE 6. 

In this system the quantity of current varies in pro- 
portion to the number of devices connected to it. 
Suppose that we are maintaining a pressure or poten- 
tial or electromotive force of no volts on such a sys- 
tem, and that we have connected to the system ten 16 
candle power incandescent lamps, consuming one-half 
19 



20 ELECTRICITY FOR ENGINEERS 

ampere each. The total quantity of current to supply 
these lamps would be 5 amperes. If we should now 
switch on ten more lamps the quantity of current 
would be 10 amperes, and the pressure would remain 
no volts. This system is also known as the "constant 
potential system," or multiple arc system, and among 
the numerous devices used in connection with it are 
the constant potential arc lamp, the shunt motor, the 
compound wound motor, the series motor, incandes- 
cent lamps, etc. Electric street railways are also 
operated on this system. The electricity supplied 
through this system of wiring may be either direct or 
alternating current. 

The series arc system, Fig. 7, is a loop; the greatest 
electrical pressure being at the terminal or terminal ends 




FIGURE 7. 

of the loop. The current in such a system of wiring is 
constant, and the pressure varies as the lamps or other 
apparatus are inserted in or cut out of the circuit. 
This system is also called the constant current system. 
The same current passes through all of the lamps, and 
the different lamps are also independent of each other. 

At the present time the series system is used mostly 
for operating high tension series arc lamps. The use 
of motors with it has been almost entirely abandoned. 

The series multiple system, Fig. 8, is simply a num- 
ber of multiple systems placed in series. This method 
of wiring was at one time employed to run incandes- 



ELECTRICITY FOR ENGINEERS 



21 



cent lights from a high tension series arc light circuit, 
but on account of the danger connected with the use 




figure 8. 

of incandescent lamps, operated from a high tension arc 
lamp circuit, the system has been abandoned. It is 
not approved by insurance companies, and conse- 
quently is not often used. 

The multiple series system consists of a number of 
small series circuits, connected in multiple, as shown 
in Fig. 9. This system of wiring is used on constant 




FIGURE 9. 



potential systems, where the voltage is much greater 
than is required by the apparatus to be used, as, for 
instance, connecting eleven miniature lamps, whose 
individual pressure required is 10 volts, into a series, 
and then connecting the extreme ends of such a series 
to a multiple circuit whose pressure is no volts. In 
electric street cars, where the pressure between the 



22 ELECTRICITY FOR ENGINEERS 

trolley wire and the running rail is 500 volts, it will be 
noticed that the lighting circuits in the car consist of 
five 100 volt lamps in series, and one end of this series 
is connected to the trolley line, the other end being 
grounded on the trucks. 

The three wire system, Fig. 10, is a system of 
multiple series. In this system, as its name implies, 
three wires are used, connected up to the machines in 





FIGURE 10, 

the manner shown in the diagram. Both machines are 
in series when all lights are turned on, but should all 
lights on one side of the neutral or center wire be 
turned off the machine on the other side alone would 
run the other lights. 

One of these wires is positive, the other is negative, 
and the remaining one or center wire is neutral. In 
ordinary practice from positive to negative wire, a 
potential of 220 volts is maintained, while from the 
neutral wire to either of the outside wires a potential 
of no volts exists. The advantages of such a system 
are many, principally among them is the use of double 
the voltage of the two wire system; this reduces the 
current one-half and allows the use of smaller wires. 
This system only requires three wires for the same 
amount of current that would require four in the other 
system. Motors are supplied at 220 volts, while 
lights operate at no. Incandescent lighting circuits 



ELECTRICITY FOR ENGINEERS 23 

can be maintained from either outside wiie to the 
neutral wire. The saving in copper by dispensing 
with the fourth wire is not the only advantage in the 
saving of conductors. The neutral wire may be much 
smaller than the outside wires because it will seldom 
be called upon to carry much current. 

Inside of buildings, however, where overheating of 
a wire is always dangerous, the neutral wire should be 
of the same size as the others. By tracing out the 
circuits in Fig. 10, it will readily be seen that, so long 
as all lamps are burning, the current passes out of 
dynamo I into the positive wire and from there through 
the lamps (always two in series) to the negative 
or — wire, returning over it to the — pole of dynamo 2. 
So long as an equal number of lamps is burning on 
each side of the neutral, no current passes over the 
neutral wire in either direction. But if the positive 
or + wire should be broken, say at a, dynamo 1 will no 
longer send current and the lamps between the positive 
and neutral wire will be out. 

Dynamo 2 will now supply the lamps between the 
neutral and the negative wire and for the time being 
the neutral wire will become positive. Should the 
negative wire break at b, the lamps connected to it 
would be out and dynamo 1 would supply the lights on 
its side, the neutral wire becoming negative. When 
motors of one or more H. P. are used on this system, 
it is usual to connect them to the outside wires using 
220 volts. It is important also to arrange the wiring 
so that an equal number of lights are installed on each 
side of the neutral. When the lights and motors are 
so arranged, the system is said to be "balanced." It 
is also very important to arrange so that the neutral 
wire cannot readily be broken. Should the neutral 



*4 ELECTRICITY FOR ENGINEERS 

wire be opened while, for instance, fifty lamps were 
burning on one side and say ten or twenty on the 
other, the ten or twenty would be broken by the excess 
voltage. Grounded wires ordinarily cause more 
trouble than anything else on electric light or power 
circuits, but with the three wire system, the neutral 
wire is often grounded. Grounds on this wire are less 
objectionable than on other wires, because it carries 
very little current, and that current is constantly vary- 
ing in direction, so that no great amount of electrolysis 
can occur at any one place. For full descriptions and 
drawings of methods of wiring, see Wiring Diagrams 
and Descriptions by Horstmann and Tousley, published 
by Frederick J. Drake & Co., Chicago. 

Feeders (see Fig. n), as the name implies, is a term 
used to designate wires which convey the current to 




any number of other wires, and the feeders become a 
part of the multiple series, multiple and three wire 
systems. 

Distributing mains are the wires from which the wires 
entering buildings receive their supply. 



ELECTRICITY FOR ENGINEERS 



25 



Service zvires are the wires that enter the buildings. 

The center of distribution is a term used for that part 
of the wiring system from which a number of branch 
circuits are fed by feeder wires. In most buildings 
the tap lines are all brought to one point, and ter- 
minate in cut-out boxes. These cut-out boxes are 
supplied by the main. Each floor of the building may 
have a cut-out box, or each floor of the building may 
have several cut-out boxes of the above description. 

Calculation of Wires. If we desire to transmit or 
deliver a certain quantity of liquid through a pipe, 
we estimate the size of the pipe and 
the comparison of sizes in the pipes 
by squaring the diameter, in inches, 
and multiplying the result by the 
standard fraction .7854. By way 
of explanation we will dwell upon 
the above method for a short time. 
In Fig. 12 we have a surface which 
measures one inch on all four 
sides, and which has an area of one square inch. 

Now in a circle which is contained in this figure, and 
which touches all four sides of the square, we would 
only have .7854 of a square inch. If the diameter of 
this circle is 2 in., instead of 1, you can readily see by 
Fig. 13 that its area is four times as great or 2 x 2 = 4. 
We then multiply by the standard number .7854 in 
order to find the area contained in the two-inch circle; 
and if the diameter were 3" in., then 3x3 = 9, and 
9 x .7854 would be the area in square inches contained 
in the three-inch circle. 

Again, if we had a square one inch in area, like Fig. 
14, and we took one leg of a carpenter's compass and 
placed it on one corner of this square, striking a 




FIGURE 12. 



26 



ELECTRICITY FOR ENGINEERS 



quarter-circle from one adjacent corner to the other 
adjacent corner, the area inscribed by the compass 
would again be .7854 of a square inch. 

The above will explain to the reader the relation 




figure 13, 

between the circular and square mil. The circular 
mil is a circle one mil (-joVo °f an inch) in diameter. 
The square mil is a square one mil long on each side. 
In the calculation of wires for electrical purposes, the 
circular mil is generally used, because we need only 
multiply the diameter of a wire by 
itself to obtain its area in circular 
mils. If we used square mils we 
should have to multiply by .7854. 

The resistance of a conductor 
(wire) increases directly as its length, 
and decreases directly as its diameter 
is increased. A wire having a diam- 
eter of one mil and being one foot 
long has a resistance at ordinary temperature of 10. 7 
ohms. If this wire were two feet long, it would have 




FIGURE 14. 



ELECTRICITY FOR ENGINEERS 27 

a resistance of 21.4 ohms, but if it were two mils in 
diameter and one foot long, it would have a resistance 
one-fourth of 10.7, or about 2.67. 

Every transmission of electrical energy is accom- 
panied by a certain loss. We can never entirely pre- 
vent this loss any more than we can entirely avoid 
friction. But we can reduce our loss to a very small 
quantity simply by selecting a very large wire to carry 
the current. This would be the proper thing to do if 
it were not for the cost of copper, which would make 
such an installation very expensive. As it is, wires 
are usually figured at a loss of from 2 to 5 per cent. 

The greater the loss of energy we allow in the wires 
the smaller will be the cost of wire, since we can use 
smaller wires with the greater loss. 

In long distance transmission and where the quality 
of light is not very important, a loss of 10 or 20 per 
cent, is sometimes allowed, but in stores, residences, 
etc., the loss should not exceed 2 or 3 per cent., other- 
wise the candle power of the lamps will vary too much. 

Where the cost of fuel is high the saving in first cost 
of copper is soon offset by the continuous extra cost 
of fuel to make up for the losses in the wires. 

To determine the size of wire necessary to carry a 
certain current at a given number of volts loss, we may 
proceed in the following manner: Multiply the num- 
ber of feet of wire in the circuit by the constant 10.7, 
and it will give the circular mils necessary for one ohm 
of resistance. Multiply this by the amperes, and this 
will give the circular mils for a loss of one volt. Divide 
this last result by the volts to be lost, and the answer 
will be the number of circular mils diameter that a 
copper wire must have to carry the current with such a 
loss. After obtaining the number of circular mils 



28 ELECTRICITY FOR ENGINEERS 

required, refer to the table of circular mils, and select 
the wire having such a number of circular mils. 
The formula is as follows: 

Feet of wire x 10.7 x amperes . . .. 

T7 —. : — r-^ = circular mils. 

Volts lost 

By simply transposing the above terms we obtain 
another formula, which can be used to determine the 
volts lost in a given length of wire of a certain size, 
carrying a certain number of amperes. 

The formula is as follows: 

Feet of wire x 10. 7 x amperes , 7 , . 

^ = ~ - = Volts lost. 

Circular mils * 

And again, by another change in the terms we 
obtain a formula which shows the number of amperes 
that a wire of given size and length will carry at a 
given number of volts lost: 

Circular mils x volts lost A 

— = — - — ;= — -. = Amperes. 

Feet of wire xio.7 

In computing the necessary size of a service or main 
wire, to supply current for either lamps or motors, it 
is necessary to know the exact number of feet from the 
source of supply to the center of distribution. When 
the distance of center of distribution is given it is well 
to ascertain whether it is the true center or not. It 
may be only the distance from a cut-out box that has 
been given, when it should have been the distance 
from the point at which the service enters the building 
or, perhaps, from the point at which the service is con- 
nected to the street mains. For when the size is deter- 
mined it is for a certain loss which is distributed over 
the entire length of the wire to be installed. The trans- 
mission of additional current on the mains in the build- 
ing increases the drop in volts in the main, and likewise 



ELECTRICITY FOR ENGINEERS 29 

in the service. Most buildings are wired for a certain 
per cent loss in voltage, estimated from the point 
where the service enters the building. All additions 
should be estimated from that point. 

In using the formula for finding the proper size wire 
to carry current, the first thing to be determined is the 
length of the wire; remember that the two wires are in 
parallel, and therefore the total length of the wire is 
twice the total distance from the commencement to 
the end of the circuit. If the proposed load on this 
circuit is given in lamps, you may reduce it to amperes, 
and if the proposed load is given in horsepower, you 
may reduce it to amperes. The voltage on the circuit 
is known in either case. You take the loss of the 
voltage and divide the product of amperes, multiplied 
by the length, as found, and 10.7 by it; this answer 
will be the size in circular mils of a wire necessary to 
carry the amperes. 

Example : What is the size of wire required for a 50 
volt system, having 100 lamps at a distance of 100 £t. , 
with a 4 per cent loss? 

Answer: The load of 100 lamps on a 50 volt system 
is 100 amperes, and a 4 per cent loss of 50 volts is 2 
volts. Multiply the total length of the wire, which is 
twice the distance, or 200 ft., by the 100 amperes of 
current; this gives us 20,000. Then multiply this by 
the constant, which is 10.7; this gives us 214,000. 
Divide this by 2, which is the loss in volts, and you 
have 107,000 circular mils diameter of wire required 

When determining the size of wire to be used it is 
always necessary to consult the table of carrying 
capacities, and this will very often indicate a wire 
much larger than that determined by the wiring for- 
mula, especially if a somewhat high loss is figured on. 



?>() ELECTRICITY FOR ENGINEERS 

When estimating the distance it is not always cor- 
rect to take the total distance. 

To illustrate: Suppose one lamp is ioo ft. from the 
point at which the distance is determined, and the 
farthest lamp is 400 ft., the remaining lamps being 
distributed evenly between these two points; we would 
average the distances between the first and last lamp, 
which would be 200 ft. It is necessary to use judg- 
ment in estimating the mean or average distance, as 
the lamps or motors are bunched differently in each 
case 

In a series system the loss in voltage makes con- 
siderable difference to the power, but does not affect 
the quality of the light as much as in a multiple arc or 
parallel system. In a parallel system the lamps 
require a uniform pressure, and this can only be had 
by keeping the loss low. In a series system the lamps 
depend upon the constant current and the voltage 
varies with the resistance, in order to keep the current 
constant. This is accomplished by a regulator on the 
dynamo, which is designed to compensate for the 
changes of resistance in the circuit and to increase or 
decrease the pressure as required. 

In estimating the size of wire for a series system you 
consider the total length of the loop. There is no 
average distance as the total current travels over the 
entire circuit. We will assume that you have an arc 
light circuit of a No. 6 Brown & Sharp gauge wire and 
want to find what loss there is in this circuit. You 
have the area of a No. 6 wire, which is 26,250 circular 
mils, and the length of the circuit, and from this we 
will figure the loss in this manner: Assuming the 
circuit to be 10,000 ft. long, and the current 10 
amperes, we will multiply 10,000 ft. by 10 amperes, 



ELECTRICITY FOR ENGINEERS 



31 



and this by 1.07, which gives us 1,070,000, and divide 
this by 26,250. The answer is 40 volts, lost in the 
circuit, 




fteeip bva\b S\oyn coracxd untt\ 






Such a circuit would operate at perhaps 2,000 or 
3,000 volts, and a loss of 40 volts would not be exces- 




32 ELECTRICITY FOR ENGINEERS 

sive. It would be wasting a little less energy than is 
required to burn one large arc lamp. 

The multiple series system is a number of small wires 
connected in multiple, and is the same as the multiple 
arc or parallel system. The wire is figured in the same 
way as for the multiple arc system. 

The series multiple system is a number of small paral- 
lel systems, and these are connected in series by the 
main wire. The wire is figured the same as for the 
series system. 

The Ediso?i three-wire system is a double multiple, and 
the two outside wires are the ones considered when 
carrying capacity is figured. When this system is 
under full load or balanced, the neutral wire does not 
carry any current, but the blowing of a fuse in one of 
the outside wires may force the neutral wire to carry 
as much current as the outside wire and it should, 
therefore, be of the same size. The amount of copper 
needed with this system is only three-eighths of that 
required for a two-wire system. 

Wiring Tables. On the following pages are presented 
wiring tables for 110,220 and 500 volt work. These 
tables are used in the following manner: Suppose we 
wish to transmit 60 amperes a distance of 1,800 ft. at 
1 10 volts and at a loss of 5 per cent. We take the col- 
umn headed by 60 in the top row and follow it down- 
ward until we come to 1,800, or the number nearest to 
it. From this number we now follow horizontally to 
the left, and under the column headed by 5 we find 
the proper size of wire, which is 500,000 c. m. The 
same current, at a loss of 10, would require only a 0000 
wire, as indicated under the column at the left, headed 
by 10. 

Before making selection of wire, always consult the 



~~ ELECTRICITY FOR ENGINEERS 33 

table of carrying capacities, page 38. This table is 
taken from the rules of the National Board of Fire 
Underwriters, and is in general use. 

The first three of the following tables are wiring 
tables for the three standard voltages, no, 220, 500 
From these tables ; can be found the sizes of wire 
required to carry various amounts of current (in am- 
peres) different distances (in feet) at several percent- 
ages of loss, or the distance the different sizes of wire 
will carry various amounts of current at several per- 
centages of loss can be found. 

These tables are figured on safe carrying capacity for 
the different sizes of wire. The distances in feet are 
to the center of distribution. 



08 












ec O {> lO rj< 

,oes 



«© ?> co lo i> oo ^ a 






3»M(OWlflM-<H 



1i>O<N(S)^a0CQ©?C.., 
x ~. r. r. -" i* - 7 » t i ~. o — -. ... - 
THi>oif3t-<st-Tj<— co £- w -* eo « e« 
O0®lOC0O!(M-rti-l 



-t'MOIX 



(O i> i- !> GO (^ !- -T X » Tl X 

THM<N^©i-coc2eo«Oi-i«£ 

lfiOiCOCO«DiOTt<OOlM(MT- 






C!OlCOCO®!DOOQOCOO»(OOOH3b 



^C»5NiH«t-l 



iB'MOlrtO^^lOlOOOrt^lRHO'M^K-: e CO O * «3 

© OJ -i-H OS C -OMOOOf'OI'WntlHHH 



m o o © © »n o © © o in o ift o o o © if: o om ©»fi - " n s k - " - 

; iOcoooo«o«n-<±ic5NMi-i' 



CJCNlO^WNW™-^ 



-5Oei3©0C«OlC"=*e0NiMi-i»-H» 



© 

r-i 


©0©©©©©-r^C}CCTtliC5Di>00©©i-ilNCC-rtliC«5 . 

§88° 






00 




coocoooiHWM^^fflNaaOHNeo^m© 

ggggg© ~~, — 

888° 






CO 
CO 






ooooooo-hnn'*ic«on»®o-'WM'^k:© 

oooo • 
ooo 




in 








OOOOOOO-WCOtlT.fflt-KO'.O^OW'O'lOe 

lll§ § ° 




IQ 








■ .OOOOOOOHt|W*K3!Oi>00«Or<WWt<ffltD ■ J. 


: :8©888° ^^^^ _ . 
: :888° 


1 






. • • .©O©C©©©-H<N00-+i>R©S>C00i©— ' W CO ■* lC to 


: : : : oooo 

• • • •©©© 

• • • -ICTPCO 







s £ 



_ o oo- • | j • 






to 


H3 


^fe§: : : 

■ • oooo ■ . • 








° n <£ 

• ... C3- 
< (V 


: : : gl!l : 

. . . ,_i — — k- h^ — — oooooo- 
■ • OW^MM-OtOOO^ffiOiiC-MM^OOOOOOO- 






Ol 
CO 


: '.'.'. ; ooo 

oooo 

^ o o o o c 






'.'.'.'.'.'. oooo 

ooooo 




oo 


W4-OI 

:.::::: o?8S 

ooooo 

— — i— — — — — OO - "': 


o 


254630 

■•.(W700 

152775 

107780 

85450 

67745 

53770 

4 2t)20 

34055 

■ (5570 

21255 

16855 

13365 

10560 

8405 

6665 

5275 

4190 

3325 

2(535 

2090 

1655 

1315 

1050 

828 

657 

526 

414 

329 

265 


b5 




127315 

101850 

76387 

53890 

42725 

33872 

26885 

21310 

17027 

13285 

10627 

8427 

6682 

5280 

4202 

3332 

2637 

2095 

1662 

1317 

1045 

827 

657 

525 

414 

328 

263 

207 

164 

132 


rf* 




6 

84877 

67901) 

50924 

35926 

28483 

22581 

17923 

14206 

11351 

8856 

7085 

5618 

4455 

3520 

2801 

2221 

1758 

1396 

1108 

878 

696 

551 

438 

350 

276 

219 

175 

138 

109 

88 




50926 

40740 

30550 

21556 

17090 

13549 

10754 

8524 

6811 

5314 

4251 

3371 

2673 

2112 

1681 

1333 

1055 

838 

665 

527 

418 

331 


O 


(J 


33950 

27160 

20370 

14370 

11393 

9032 

7170 

5682 

4540 

3542 

2334 

3247 

1782 

1413 

1120 

888 

703 

558 

443 

351 




3 


25463 
20370 
15275 
10778 
8545 
6774 
5377 
4262 
3405 
2657 
2125 
1685 
1336 
1060 
840 
666 
527 
419 


to 

o 


CD 

H3* 


20370 
16295 
12222 
8622 
6836 
5420 
4302 
3410 
2724 
2125 
1700 
1348 
1050 
848 
672 
533 
422 


to 


o H 

K 


16975 
13580 
10183 
7185 
5696 
4516 
3585 
2841 
2270 
1771 
1417 
1123 
891 
706 
560 
444 


co 
© 


12731 

3 0185 
7637 
5389 
4272 
3387 
2688 
2131 
• 1702 
1328 
1062 
842 
668 
530 
420 


© 


5g 

CD p 


10185 
8147 
6111 
4311 
3418 
2710 
2151 
1705 
136i 
1062 
850 
614 
525 
424 
...... 


© 




60 

8487 

5091 
3592 

2848 
2258 
1792 
1 120 
1135 
885 
708 
562 


P 

I® 




80 

:.. 166 

5092 

19 

2695 
2136 
1679 
1344 
10(55 
851 
664 
.. . 




100 

5092 
4073 
3055 
2155 
1709 
1355 
1075 
852 
681 


> 

B 




120 

I ■ 

2516 
1796 
1424 
1129 
896 
710 




160 

3183 
2546 
1910 

1068 
839 


(T> 




200 

2516 

2030 
1528 
1077 

.... 




250 

2037 
1629 
1222 




llll 










5, 


CO 





CD 

g 
< 

o 
f-i 

0) 

■2- 
|$ 

5.2 

«= o 

CD f3 
£3 

SO 
II 

■si 

cs© 
HW 

-rH 6 
2H 

M> 

s 

ft 

O 
Eh 

.§ 

En 


o 
o 

CO 


Ifi-T CON 












o 


6800 
5420 

4(85 
2882 
2285 










o 
in 

rH 


7716 
6142 
4629 
3260 
2589 
2054 










120 

9645 

7677 
56(52 
4082 
3236 

2567 

1606 








100 

11574 
9213 
6944 
4898 
3884 
3080 
2443 
1928 
1531 








o 


14467 
11516 
8680 
6123 
4855 
3850 
3055 
2410 
1914 
1522 






o 


19290 
15355 
11324 
8165 
6473 
5134 
4073 
3213 
2552 
2 '30 
1610 
1276 






o 


23148 
18426 
13888 
9797 
7768 
6161 
4887 
3856 
SOPS 
2436 
1932 
151] 
1218 
966 






o 


28935 
23032 
17361 
12247 
97Ki 
7701 
6110 
4820 
3828 
3045 
2415 
1914 

1207 

957 






o 


38580 
C0710 
22648 
16330 
12947 
10268 
8146 
6427 
5104 
4061 
3220 
2552 
2030 
1610 
1276 
1015 






20 i 25 

57870 46296 
46064 36852 
34722 27777 
24495 19595 
19421 15537 
15402 12322 
12221 9775 
9640 7712 


6125 
4873 
3864 
3062 
2436 
1932 
1531 
1218 
978 






7656 
6091 
4831 
3828 
3045 
2415 
1914 
1522 
1207 
957 






IO 


77160 
61420 
45296 
32660 
25895 
20536 
16293 
12854 
10208 
8122 
6441 
5104 
4061 
3220 
2552 
2030 
1610 
1276 
1018 
805 






© 


115740 
92129 
69444 
48990 
38843 
30805 
24442 
19281 
15313 
12183 
9662 
765(5 
6091 
4831 
3828 
3045 
2415 
1914 
1527 
1207 
957 
763 






CD 


192900 

153550 

115740 

81650 

64738 

51341 

40736 

32135 

25521 

20305 

16103 

12760 

10152 

8051 

6380 

5076 

4026 

3190 

2546 

2013 

1595 

1273 

1005 

797 

636 

: 503 

398 

316 

253 

199 


«* 


389350 
230322 
173610 
122475 
97107 
77012 
61105 
48202 
382S2 
30457 
24155 
19140 

12077 
9570 
7614 
6039 
4785 
3819 
3019 
2392 
1910 
1510 
1195 
950 
755 
597 
475 
377 
298 


<N 


578700 

460645 

347220 

244950 

194215 

154025 

122210 

96405 

76565 

60915 

48310 

38282 

30457 

24155 

19140 

15229 

12077 

9570 

7039 

6039 

4785 

3819 

3019 

2392 

1910 

1510 

1195 

950 

755 

597 


5| • 
3 o a) 

-. © M> 

2m^ 

P Ml o 

bos g 


O 
i-H 

CO 


coooooo-«M*ii3fflc-xcf.o--nM*in» • • • 
ooooo tH '""' '~ l "" '"' *"* " • • ■ 

oSo° : : : 




OOOOOOOHNMtiOiDMBaO-WM^iOS • • 

ll| S ° : ! : 




1 QOOOOOO — NCO-^lftCOt-aOCSO'rtNeOTjdntO ■ 
<0 . OOOO ; 

i ' m-<t<eo 




ta 




■ OOCOOOC-WWfiKSt.MOlOtHNm^ifitO . 

:§H§oo ~~~~~ . 

• in^co : 




CO 








;r;oooo-w«'*ii:(Bi>«»o-«wi'iflfO • 
§§g§§° ^ rt -~„„ . . 

SS3 : ■ 


w 








• :| 


OCOCOC-'NMTiKBt-OOa 

l|s s ° 

"J>CO 


Or-NCO 


TflCHO 



jsiP4*.cofcS"0-.ooo<]Oi£n>*>.coM 



- OOO ©■ 



t _ C JO 00 

© ^j *^ ^ © © ' "~ 

■»'-> ■*. CO00 5C )i _■■-_-_.:_' . •*- o 10 on oi 



ooocoooooo 



s§8£ 



Sm© 

9il £° :X -I ^" '■ • ' " v"icr.aa.^;oooiooo 

QOWO^JtcWOOiOO-SiC- i o o © o O 

0!^^W©MQM^-5"J'WO!OI|C010'000000 

<; os os o >fr. i— ^ 



hoh - — -3 oc on <s >-» 01 —' -3 

to on to as to oi w oo os *>- — so ' . .. - a to «p to gs o 

00-JWMOO-JWi(i.»©-JQO*©OM"JOOOOOO 
OS 00 *>■ >-» OS O tO 



Circular 

Mils 



Square Mils 



►-;• os- o»- en 



^ 01 U M 



Pounds 
per 1000 feet 



00»«<0t( 



Pounds 
per mile 



a os eo o -3 to * 



Feet per 
Pound 



Pounds 
per 1000 feet 



WOOimok 



Pounds 
per Mile 



§ 52 



<x<tos*.4>.oototo^>-i 

00*.mOOOMWOO)C05D<!Oi 
- - 1 on to 00 -1 h^ O OS <! 



-^oixj^ooa 



Feet 

per Pound 



<s?oi\3on«o 
oooo^oj^j 



ooooonoo?ooo©^c 
Go<tosoo©to*-too 



»oooo 



Pounds 
per 10 feet 



*-p-'M(JMW*.0'aa)OMG- OS CO © *>■ to 
*0'»00OW0'.O0)W"ii : , <S -I OS GO 4-^ 

►— ►-»0n.N*-<5CnaeC0tOGCaOOn©O0On4».CO-<l<aiOO©~3 

wsoonas^ooascooo^-oopsoasGOfcaovoo-cj 



soccffim^osMM^ 



s>OO0O— ©OOOOCOnc 



Pounds 
per Mile 



Feet 

per Pound 



-ootooa 



,0GC-Ci~5^^0n« 



ROhms 
per 1000 feet 



>— osoooooo 
toccooona 

WMOffloa 



K-jffiow»m»)ooocac 



Ohms 
per Mile 






OOCI^OOpOiUiOi-W-DMCOiOO*-^^^ 



Feet 
per Ohm 



OIMMhCOOOOOOCOOC 



SII-311 



. . . 

»©COOS 



" 



Ohms 
per Pound 



38 ELECTRICITY FOR ENGINEERS 

TABLE OF CARRYING CAPACITY OF WIRES. 
UNDERWRITERS' RULES. 
TABLE A. TABLE B. 

Rubber Other 

Insulation. Insulations. Circular 

B. & S. G. Amperes. Amperes. Mils. 

iS 3 5 1,624 

16 6 8 2,583 

14 12 16 4,107 

12 17 23 6,530 

10 24 32.., 10,380 

8 33 46 16,510 

6 46 65 26,250 

5 54 77 33,ioo 

4 65 92 41,740 

3 76 no 52,630 

2 90 131 66,370 

1 107 156 83,600 

o 127 185 105,500 

00 150 220 133,100 

000 177 262 ,. 167,800 

0000 210.... 312 211,600 

Circular Mils. 

200, 000 200 300 

300, 000 270 400 

400,000 330 500 

500,000 390 590 

600,000 450 68o- 

700,000 500 760 

800,000 550 840 

900,000 600 920 

1,000,000 650 1,000 

1,100,000 690 1,080 

1,200,000 730 1,150 

1,300,000 770 1,220 

1,400,000 810 1,290 

1,500,000 850 1,360 

1,600,000 890 1.430 

1,700,000 930 1,490 

i,8oo,oco 970 i,55o 

1,900,000 1,010 1,610 

2,000,000 1,050 1,670 

The lower limit is specified for rubber-covered wires 
to prevent gradual deterioration of the high insula- 
tions by the heat of the wires, but not from fear of 
igniting the insulation. The question of drop is not 
taken into consideration in the above tables. 



ELECTRICITY FOR ENGINEERS 39 

TABLE OF DIMENSIONS OF PURE COPPER WIRE.* 







Arfia. 


Weight and Length. 


No. 


Diam. 
Mils. 








Sp. Gr. 8.9. 




B. & S. 


Circular 


Square 


Lbs. 


Lbs. 


Feet 






Mils. 


Mils. 


per 
1000 feet. 


per 

Mile. 


per 
Pound. 


0000 


460.000 


211600.0 


166190.2 


640.73 


3383.04 


1.56 


ouo 


409.640 


167805.0 


131793.7 


508.12 


2682.85 


1.97 


00 


364.800 


133079.0 


104520.0 


402.97 


2127.66 


2.48 





324. 950 


105592.5 


8i932.2 


319.74 


1688.20 


3.13 


1 


289. aoo 


83694.5 


65733.5 


253.43 


1338.10 


3.95 


2 


257.630 


66373.2 


52129.4 


200.98 


1061.17 


4.98 


3 


229.420 


52633.5 


41338.3 


159.38 


841.50 


6.28 


4 


204.310 


41742.6 


32784.5 


126.40 


667.38 


7.91 


5 


181.940 


33102 2 


25998.4 


100.23 


529.23 


9.98 


6 


162.020 


26250.5 


20617.1 


79.49 


419.69 


12.58 


7 


144.280 


20816.7 


16349.4 


63.03 


332.82 


15.86 


8 


128.490 


16509.7 


12966.7 


49.99 


263.96 


20.00 


9 


114.430 


12094.2 


10284.2 


39.65 


209.35 


25.22 


10 


101.890 


10381.6 


8153.67 


31.44 


165.98 


31.81 


11 


90.742 


8234.11 


6407.06 


24.93 


137.65 


40.11 


12 


80.808 


6529.94 


5128.60 


19.77 


104.40 


50.58 


13 


71.961 


5178.39 


4067.07 


15.68 


82.792 


63.78 


14 


64.084 


4106.76 


3225.44 


12.44 


65.658 


80.42 


15 


57 068 


3256.76 


2557.85 


9.86 


52.069 


101.40 


16 


50.820 


2582.67 


2028.43 


7.82 


41.292 


127.87 


17 


45.257 


2048.20 


1608.65 


6.20 


32.746 


161.24 


18 


40.303 


1624.33 


1275.75 


4.92 


25.970 


203.31 


19 


35.890 


1288.09 


1011.66 


3.90 


20.594 


256.39 


20 


31.961 


1021.44 


802.24 


3.09 


16.331 


323.32 


21 


28.462 


sio.oa 


636.24 


2.45 


12.952 


407.67 


22 


25.347 


642.47 


504.60 


1.95 


10.272 


514.03 


23 


22.571 


509.45 


400.12 


1.54 


8.1450 


648.25 


24 


20.100 


404.01 


317.31 


1.22 


6.4593 


817.43 


25 


17.900 


320.41 


251.65 


.97 


5.1227 


1030.71 


26 


15.940 


254.08 


199.56 


.77 


4.0623 


1299.77 


27 


14.195 


201.50 


158.26 


.61 


3.2215 


1638.97 


28 


12.641 


159.80 


125.50 


.48 


2.5548 


2066.71 


29 


11.257 


126.72 


99.526 


.38 


2.0260 


2606.13 


30 


10.025 


100.50 


78.933 


.30 


1.6068 


3286.04 


31 


8.928 


79.71 


62.603 


.24 


1.2744 


4143.18 


32 


7.950 


63.20 


49.639 


.19 


1.0105 


5225.26 


33 


7.080 


50.13 


39.369 


.15 


.8015 


6588.33 


34 


6.304 


39.74 


31.212 


.12 


.6354 


8310.17 


35 


5.614 


31.52 


24.153 


.10 


.5039 


104; 8.46 


36 


5.000 


25.00 


19.635 


.08 


.3997 


13209.98 


37 


4.453 


19.83 


15.574 


.06 


.3170 


16654.70 


38 


3.965 


15.72 


12.347 


.05 


.2513 


21006.60 


39 


3.531 


12.47 


9.7923 


.04 


.1993 


26487.84 


40 


3.144 


9.88 


7.7635 


.03 


.1580 


33410.05 



*1 mile pure copper wire 13.59 ohms at 15.5° C. or 

1-16 in. diam. ~ 59.9* F. 

1 circular mil is .7854 square mil. 



CHAPTER III 

Current Generation in Dynamos — Dynamos — Brushes and 
Commutators. 

Current Generation in Dynamos. If we take a coil of 
wire, Fig. 15, and rapidly thrust a magnet into it, we 
shall observe a certain deflection of the galvano- 
meter needle shown with it. This deflection con- 
tinues only while the magnet is in motion. After 




FIGURE 15. 



we have inserted the magnet and it has come to 
rest the galvanometer needle will return to its normal 
position. When we withdraw the magnet the deflec- 
tion of the needle will be in the opposite direc- 
tion. If the magnet is inserted or withdrawn with 
a veiy quick motion, the deflection will be consider- 
able. If the magnet is very slowly inserted or with- 
drawn the deflection will hardly be noticeable. The 
40 



ELECTRICITY FOR ENGINEERS 



41 



same phenomena will occur if instead of moving the 
magnet, we hold it stationary and move the coil, or if 
both of them be moved towards or from each other. 
The deflection of the compass needle indicates that a 
current of electricity is passing along the wire, and the 
experiments above described show exactly how cur- 
rents of electricity are produced in dynamos. 

An electromotive force is induced by rapidly cutting 

"lines of force," that is, by moving either a magnet 

over a wire or a wire over or near a magnet. The 




current in turn is the result of this electromotive force 
acting in a closed circuit. A bar of iron becomes an 
electromagnet if we wind about it a few turns of wire 
and cause a current of electricity to flow along the 
wire, Fig. 16. The magnetism is conceived to consist 
of lines of force, which leave the bar at one end and 
enter it at the other, the direction of these lines 
depending upon the direction in which the current 
circulates about the bar of iron. The number of these 
lines of force depends upon the number of ampere 
turns in the iron bar and on the diameter, length and 
quality of the iron bar. 



42 ELECTRICITY FOR ENGINEERS 

Ampere turns is a term used to indicate the mag- 
netizing force; it is the number of turns of wire on a 
magnet multiplied by the current in amperes flowing 
through these turns of wire. 

Haskins, in Electricity Made Simple, explains this 
thus: "If, for instance, we have a current of one 
ampere flowing through a single turn of wire around a 
bar of soft iron and we have developed enough mag- 
netism to lift a keeper or other piece of iron, weighing 
one ounce, then with one-half the amount of current 
and two coils around the bar, we would obtain the 
same result, and with three turns of wire we would 
require but one-third the current to develop the same 
lifting power in the bar or magnet." 

The law of magnetic flow is very much the same as 
the law of current flow. If the iron bar is of low mag- 
netic resistance, the flow will be quite great; if of high 
resistance, the flow will be small. 

Lines of force can also be shunted just as a current 
of electricity can; that is, they will follow the path of 
lowest resistance just as a stream of water or a current 
of electricity will. 

Now let us consider the elemental sketch of a 
dynamo, Fig. 17. The wire a represents the armature 
and we have also the iron bar and the coil of wire 
wound on it and, for the present, we may consider the 
battery B as the source of the current which produces 
the magnetism or lines of force in the iron bar. The 
battery current magnetizes the iron bar (which in 
dynamos is known as the field magnet) and produces 
the lines of force indicated by arrows. 

These lines of force leave the field magnet of our 
dynamo at the north pole marked N, and pass through 
the air-gap and armature into the south pole marked S. 



ELECTRICITY FOR ENGINEERS 



43 



As we begin to move the wire or armature, it cuts 
through these lines of force and begins to generate an 
electromotive force, which in turn will cause the cur- 
rent to flow if the circuit is ciosed through a lamp or 
other device. 

This current reverses in direction as the wire a passes 
from the influence of the south pole into that of the 
north pole and the brushes B' and B", which transmit 




FIGURE 17. 



the current to the outside wires, are so set that they 
change the connection of the wire a at the time that it 
passes from one pole to the other. By this means the 
current in the external circuit is kept constant in 
direction, although it alternates in the armature. 

The faster we turn our wire or armature, the greater 
will be the electromotive force generated. Instead of 
using onlv one wire, as in Fig. 17, we may take many 



44 



ELECTRICITY FOR ENGINEERS 



turns before bringing the end out, and in so doing 
obtain the well known drum armature, or, by a slightly 
different method of winding, the gramme ring arma- 
ture, Fig. 18. Here we have many wires cutting the 
lines of force at once and our electromotive force with 
the same number of revolutions of the armature is cor- 
respondingly increased, and the more turns of wire we 
arrange to cut those lines of force per second the 
greater will be our E. M. F. Instead of providing 




FIGURE 18. 



more wire or increasing the speed of our armature we 
can increase the magnetism, or number of lines of force, 
by sending more current through the fields, that is 
increasing the "ampere turns." 

If we wish to reverse the current flow we can do so 
by revolving the armature in the opposite direction, 
or by reversing the current through the fields. 

Dynamos. Having so far considered the generation 
of currents in dynamos, we may now consider different 
types of dynamos and their uses. Fig. 19 shows adia- 



ELECTRICITY FOR ENGINEERS 



45 



gram of the wires and connections of a series dynamo. 
The principal use of this dynamo at present is in con- 
nection with series arc circuits. (See Fig. 7.) This 
dynamo is usually equipped with an automatic regu- 
lator (which will be explained later) to raise or lower 
the voltage as the number of lamps increases or 




figure 19. 



decreases, the current remaining constant at about 10 
amperes. By reference to the figure, we can trace the 
current as it flows from the 4- brush, in the direction of 
the arrows, around both field magnets and through the 
lamps, returning to the - brush on the dynamo. In 
our elementary sketch of a dynamo we used battery 
current to magnetize our fields; we need not consider 



46 



ELECTRICITY FOR ENGINEERS 



that any more, for in practice all direct current 
dynamos produce their own magnetism by circulating 
some or all of their current through the field coils. 

In the shunt wound dynamo, Fig. 20, the wire in the 
field winding is of such size and connected in such a 
manner as to have a resistance so high that only a 




^mtrf) 



FIGURE 20. 



portion of th(^ main generated current of electricity 
passes around the field magnets. The quantity of cur- 
rent passing around these field magnets is also regu- 
lated by a resistance sometimes called a rheostat shown 
at R. The resistance to the flow of current through 
this box is adjusted by hand by the attendant and the 
flow of current through this rheostat and around the 






ELECTRICITY FOR ENGINEERS 4? 

field magnet is what determines the electromotive force 
of the dynamo. 

This type of dynamo is used for electric lighting and 
for operating motors. The electromotive force of such 
a dynamo remains nearly constant, but the current 
varies with the number of lights or motors used. If it 
were connected to too many lights it would deliver too 
much current and become overheated and perhaps 
burn out. The current leaves at the + brush, passes 
through whatever lamps happen to be switched on and 
returns to the — brush. 

Fig. 21 shows a diagram of a compound wound 
dynamo. This is really a combination of the series 
and shunt dynamos. If the current in a series dynamo 
is not kept constant the magnetism in the fields will 
vary as the current varies, and consequently its volt- 
age will be very unsteady. This makes such a dynamo 
unfit for use with variable currents. 

The voltage of a shunt dynamo is quite constant with 
variable loads, but still it leaves much room for 
improvement; not because of any variation in the 
induced electromotive force, but because of the losses 
occurring in the armature and wires conveying current. 
The loss of voltage in the armature and line equals the 
current multiplied by the resistance; consequently, as 
the current increases more and more volts are lost and 
the pressure goes down. If we would have the pressure 
remain at its normal value, we must find some way to 
increase the field magnetism as the current delivered 
by the dynamo increases, and this is the purpose of 
the compound winding. The compound winding car- 
ries the total current of the dynamo around the fields, 
but only a few times, just often enough so that the 
increase in magnetism resulting from this current may 



48 



ELECTRICITY FOR ENGINEERS 



make up for the loss in the armature or line. Dyna- 
mos may be compounded for any per cent, of loss 
desired. 

The foregoing descriptions are those of direct cur- 
rent dynamos, and they are called direct or continuous 




FIGURE 21. 



current dynamos because the current flow continues in 
one direction out of the positive or + side of the 
dynamo, to the external circuit, and back again to the 
negative or - side of the dynamo. The current as it 
is generated in the coils of the armature which 



ELECTRICITY FOR ENGINEERS 49 

revolves between the field or pole pieces, is alter- 
nating; that is to say, if the armature wires were con- 
nected to collector rings the current in the outside 
wires would be reversed every time the position of the 
wire in the armature were changed from the influence 
of one pole piece to that of the other. If the coils 
constituting the armature are connected to a device 
called the commutator, they will be commutated or 
rectified. 

Such a commutator is formed of alternate sections of 
conducting and non-conducting material, running 
parallel with the shaft with which it turns. It is 




FIGURE 22. 

placed on the shaft of the armature so that it rotates 
with it, as shown in Fig. 22. The brushes press upon 
its surface and collect the current from the bars. (See 
Fig. 31.) The function of the commutator is to change 
the connections of the armature coils from the + or 
positive to the negative or — side of the circuit at the 
time at which the coil connected to the bar under the 
brush passes from the influence of one pole piece into 
that of the other. This is the time at which the cur- 
rent in the coil reverses in direction, and is called the 
neutral point. If we consider, for the sake of simplic- 
ity, an armature having only one turn of wire on it, 
as Fig. 17, there will be a time while the coil is in the 



50 ELECTRICITY FOR ENGINEERS 

position indicated by dotted lines at c and d when no 
current is being generated. The brushes on any 
dynamo should always be set at this point, for this is 
the point of least sparking. In actual practice all 
commutators have quite a number of bars and it is 
impossible to avoid, in passing under the brushes, that 
at least two of them are in contact with a brush at the 
same time. If a brush did leave one bar before it 
touches another, the current would be entirely broken 
for that length of time and much sparking would 
result. The nature of all armature windings is such 
that while the brush is in contact with the commutator 
bars it short circuits that coll between them. This is 
the main reason why the brushes must be kept at a 
point at which the coil which is short circuited gener- 
ates no current. 

Although the electromotive force generated in one 
coil of a dynamo is very small, the resistance of the 
"short circuit" formed by the dynamo brush is also 
very small and therefore the current may be quite large. 
This current is the main cause of sparking in dynamos. 
The number of bars constituting a commutator depends 
upon the winding of the armature, and the number of 
coils grouped thereon. By increasing the number of 
coils and commutator sections the tendency to spark 
at the brushes is decreased, and the fluctuations of the 
current are also decreased. However, there are many 
reasons against making the number of bars on a com- 
mutator very great. Increasing the number of bars in 
a commutator increases the cost of manufacture, and 
in smaller dynamos if the number of bars be increased 
beyond a certain extent, each bar becomes so thin 
that a brush of the proper thickness to collect the cur- 
rent from the commutator would lap over too many 



ELECTRICITY FOR ENGINEERS 51 

bars of the commutator at one time. Each commu- 
tator bar should be of the size that will present suffi- 
cient metal for the carrying capacity of the current 
generated in the coil to which it is connected. Differ- 
ent builders of dynamos have different ideas as to the 
number of amperes that maybe carried per square inch 
in a commutator bar, but where a commutator is made 




FIGURE 23. 



of 95 per cent, copper it is usual to allow for each ioo 
amperes a commutator bar surface of i% sq. in. 

The method of electrical connection between the 
commutator bar and the coil of the armature varies in 
different designs. Some builders solder the terminals 
of the coils to the commutator bars; others bolt the 
terminals of the coils to the bars; and some makers 
use hard drawn copper and "form" the armature coii 
in such a manner that both ends of the coil become 



5 L Z ELECTRICITY FOR ENGINEERS 

commutator bars, making the coil continuous from one 
end of the commutator bar to the end of the diametric- 
ally opposite commutator bar. 

In Fig. 23 we show a so-called "formed" armature 
coil, after it has been prepared by properly insulating 
it and bending it into shape ready to be applied to the 
laminated armature body. 

In Fig. 24 is shown a "formed" coil armature with 




FIGURE 24. 



the winding almost finished. The commutator is yet 
to be placed on the shaft and the coil terminals con- 
nected to the commutator bars. 

In Fig. 25 we have an armature shaft with the lami- 



figure 25. 

nated armature body keyed on to the shaft ready to be 
wound. 



ELECTRICITY FOR ENGINEERS 53 

The body on which the armature coils are to be 
wound is made up of sheet iron punchings and placed 
on the armature shaft in the same manner that you 
would put ordinary iron washers on a lead pencil. 
These punchings or discs are insulated from one 
another by having previously been painted with a coat 
of shellac; for there is the same tendency to produce 
current in the iron part of the armature, due to the 
cutting of the magnetic lines, as there is in the copper 
wire which is wound on its surface. If the iron core 
were solid, there would be a very large current circu- 
lating in the same direction as that which flows through 
the wires. Such a current would be entirely useless 
and would heat the armature; to prevent this the 
armature is built up of thin sheet iron discs. 

Brushes and Commutators. Figs. 26 to 30 show differ- 
ent arrangements of modern brushes and brush-holders. 
These are used to take the current from the commu- 
tator and deliver it to the outside wires in the case of a 
dynamo, and for the opposite in the case of a motor. 

There are many different designs and constructions 
of brushes and brush-holders, and these designs are 
brought about by the various ideas of different builders 
in their attempt to produce various advantageous 
results, but the electrical connections and underlying- 
principles remain the same whether a copper or a car- 
bon brush be used. 

In any construction of brush holding device, if great 
care is not exercised in keeping it thoroughly clean, 
trouble is sure to be the result, and trouble of this 
nature increases so rapidly that unless the attendant 
immediately sets about to right it, a burned out arma- 
ture is almost sure to be the consequence sooner or 
later. In alternating current dynamos, where brushes 



"A ELECTRICITY FOR ENGINEERS 

rest on collector rings instead of commutators, it is 
much easier to keep out of trouble, because the 
brushes in this case merely collect the current from 
the rings and do not commutate or rectify it. 

The brushes and commutator of a dynamo or motor 




figure 26. 



are probably the most important parts with which the 
engineer has to deal. Great care should be taken that 
the brushes set squarely on the commutator and that 
the surface of the brushes and commutator are as 
smooth as possible. It is a good plan, and in some 



ELECTRICITY EOR ENGINEERS 



55 



cases the brush-holders are so made, that the brushes 
set in a staggering position, that is to say, in a posi- 
tion so that all the brushes will not wear in the same 
place over the circumference of the commutator and 




-^ZS 



FIGURE 27. 



cause uneven wear across the length of the commutator 
bars. In most machines the armature bearing is left 
so that there is more or less side motion, which, when 
the armature is running, causes a constant changing of 
the position of the brushes and commutator. 



56 



ELECTRICITY FOR ENGINEERS 



Whatever style of brush is used, the commutator 
should be kept clean and allowed to polish or glaze 
itself while running. No oil is necessary unless the 
brushes cut, and then only at the point of cutting. A 
cloth (not cotton waste) slightly greased with vaseline 
and applied to the surface of the commutator while 




figure 28. 



running is best for the purpose of preventing the com- 
mutator from cutting. Should the commutator 
become rough, it should be smoothed with sandpaper, 
never using emery cloth, because emery cloth is con- 
ductor of electricity, and the particles of emery are 
liable to lodge themselves between the commutator 
bars in the mica and short circuit the two bars, thereby 



ELECTRICITY FOR ENGINEERS 57 

burning a small hole wherever such a particle of emery- 
has lodged itself. The emery will also work into the 
brushes and copper bars and wear them down; it being 
almost impossible to remove all the emery. 

In the end-on carbon brushes, Fig. 30, the contact 
surface of the brushes should be occasionally cleaned 
by taking a strip of sandpaper, with the smooth side 
of the paper to the commutator, and the sanded side 
toward the contact surface of the brush, and then by 




FIGURE 29. 

leaving the tension of the brush down on the sand- 
paper, it is an easy matter to move the sandpaper to 
and fro and throughly clean off the glazed and dirty 
surface from the carbon, leaving it with a concave that 
will exactly fit the commutator. 

The advantages of carbon brushes are many. 
Among the cardinal points are: The armature may 
run in either direction without it being necessary to 
alter the brushes; the carbon can be manufactured with 
a quantity of graphite in its construction, thereby 



58 



ELECTRICITY FOR ENGINEERS 



lowering the mechanical friction of the brushes on the 
commutator; they do not cut a commutator so much 
by sparking; the commutator has a longer life, the 
wear being more evenly distributed. 

Carbon brushes, due to their rather high resistance, 
will often heat up considerably, but, although this 
heat is objectionable, their resistance tends to cut 
down the sparking. The brushes are sometimes coated 
with copper to reduce their resistance. Often a car- 




FIGURE 30. 



bon brush will be found which is very hard. As a rule 
such a brush should be thrown away, as it will heat 
abnormally and at the same time wear the commu- 
tator. 

In Fig. 31 we have one of the various so-called old 
styles of leaf brush-holders. The end-on brushes are 
more generally used in modern practice, because their 
contact surface area is not increased or decreased by 
wear. Consequently the brushes always remain in a 
diametrically opposite position. With the old style 



ELECTRICITY FOR ENGINEERS 



59 



brush-holding device, where the brushes rest on the 
commutator at a tangent, great care should be exer- 




FIGURE 31. 



cised not to allow the brushes to wear in a position so 
that their points will be out of diametrical opposition. 







FIGURE 32. 



In Fig. 31 we show the correct way that this type of 
brush should be set. 



00 ELECTRICITY FOR ENGINEERS 

In Figs. 32 and 33 we show the incorrect way. 

By remembering that each one of the commutator 
bars is the end of a coil, and then just mentally tracing 
the current through the coils from one brush to the 
other, we can readily understand what the results are 
when the brushes are neglected and left in a relative 
position, as shown in these figures. 

Sparking is the usual result of brushes allowed to 
wear to such an extent. Overloading of a dynamo or 
motor will also cause serious sparking, and no amount 




figure 33. 

of care can prevent damage to armature, commutator 
or brushes, if a machine is permitted to be overloaded. 
Sometimes the commutator will contain one or more 
bars which, as the commutator gets old and wears 
down, will wear away either too fast or too slow, due 
to the metal being harder or softer than the rest of the 
bars forming the commutator. This causes a rough- 
ness of the commutator and results in the flashing of 
the brushes and heating of both the commutator and 
brushes. About the only satisfactory method of 



ELECTRICITY FOR ENGINEERS 



61 



remedying this evil is to take out the armature and 
have the commutator turned down in a lathe. 

A short-circuited coil in the armature, or a broken 
armature connection, will also cause considerable 
sparking. Either of these conditions can be located 
by means of a Wheatsone bridge or by what is known 
as the fall of potential method. To make a test with 
this latter method, connect in series with the armature 
to be tested some resistance capable of carrying the 
necessary current, also an ammeter. Some apparatus 
for varying the current strength, such as a water rheo- 





M^.MS 






















A / \A A A 


—C\- 


10 ■ ff n" 






WR 






vvvvv 


VA>- 


xv v y J? 



FIGURE 34. 



stat or lamp rack, must be connected in the circuit, a 
diagram of which is shown in Fig. 34. 

In the diagram, WR is the water rheostat or lamp 
rack, R the known resistance, A the ammeter and M 
the armature to be tested. By means of the water 
rheostat regulate the -current passing over the appa- 
ratus until it is of such strength that a deflection can 
be obtained on a voltmeter when it is connected to two 
adjacent bars on the commutator. Suppose the arma- 
ture coil between bar 1 and 2 on the commutator were 
broken. The voltmeter connected across these two 
bars would give the same reading as when connected 



62 ELECTRICITY FOR ENGINEERS 

across the two points 10 and 11. If the voltmeter were 
connected between any other two points on the com- 
mutator on the same side as the broken coil no deflec- 
tion would be obtained, while connecting the voltmeter 
between any two adjacent bars on the other side of the 
commutator would give practically the same reading 
irrespective of which bars were used. The resistance 
of one or more sections of the armature winding could 
also be found by using Ohm's law, R = E/C, or the 
resistance would be equal to the voltage divided by the 
current as shown on the ammeter. It must be remem- 
bered that this latter will be true only when there is an 
open coil in one side of the armature, for in this case 
only will the whole current flow through the one side. 
If the coil between bars I and 2 were short circuited, 
the voltmeter would show practically no reading 
between these bars; while between any other bars some 
deflection would be obtained. An open circuit or 
short circuit will nearly always be found by examina- 
tion, as the trouble usually happens very close to the 
commutator connections in the case of an open circuit 
and may very often be found between the commutator 
bars themselves, in the case of a short circuit. If the 
trouble is not at these places it will usually be in the 
windings, in which case the only remedy is to have it 
re-wound. Temporary repairs may be made in the case 
of an open circuit by short circuiting the commutator 
bars around the open circuit, but this method should 
only be used in emergency, as the sparking will in time 
destroy the commutator. 

With many dynamos, especially of older types, it is 
necessary to shift the brushes with every change of 
load. The current produced by the armature makes a 
magnet out of it and the magnetism of the armature 



ELECTRICITY EOR ENGINEERS 



63 



opposes that of the fields. In Fig. 35 the armature is 
working with a very light load and the lines of force 
of the field magnets are only slightly opposed by those 




FIGURE 35. 



of the armature. In Fig. 36 we assume a heavy load 
on the dynamo and consequently the magnetism of the 
armature opposes that of the fields. This changes the 
location of the neutral point (when the coils under the 
brush generate no current) and it becomes necessary to 




FIGURE 36. 



shift the brushes accordingly, or great sparking would 
result. The amount of shifting necessary with changes 
of load varies in different dynamos. If the field is 



64 ELECTRICITY FOR ENGINEERS 

very strong compared to the armature, it will be but 
little. If the armature (as in some arc dynamos) is 
very strong compared to the field, it will be consider- 
able. 

In dynamos, with increasing load, the brushes should 
be shifted in the direction of rotation and in the oppo- 
site direction when the load decreases. 

Never allow a dynamo or motor to stand in a damp 
place uncovered. Moisture is apt to soak into the 
windings and cause a short circuit or ground when 
started. Great care should also be used should it ever 
be found necessary to use water on a heated bearing. 
If the water is allowed to reach the armature or com- 
mutator, it is bound to cause trouble. Water should 
only be used in case of emergency, and then sparingly* 



CHAPTER IV 
OPERATION OF DYNAMOS 

Constant Potential Dynamos. In order to thoroughly 
explain the operation of dynamos, let us assume that 
we have the task of starting a new shunt dynamo, one 
that has never generated any current. Our first step is 
to open the main switch and turn the rheostat or field 




FIGURE 37. 

resistance box so that all the resistance is in circuit. 
A rheostat consists of a number of resistances, Fig. 37, 
so arranged that they can be cut in or out of the circuit 
without opening the circuit. By reference to the figure 
it will be seen that the current enters at the handle and 
from there passes to the contact point upon which the 
65 



()() 



ELECTRICITY FOR ENGINEERS 



handie happens to rest. If the handle is at i the cur- 
rent must pass through all the wire in the box; if it is 
at 2 it simply passes through the handle and out. 

Rheostats for the shunt circuit of a dynamo should 
have sufficient resistance, so that when it is all inserted 
the voltage of the dynamo will slowly sink to zero. 
This method of stopping the action of a dynamo is 




FIGURE 37. 



perfectly safe and should be followed wherever pos- 
sible. 

We are now running our dynamo with all resistance 
in the shunt circuit. This is simply as an extra pre- 
caution because we know nothing about this particular 
dynamo. When it is known that the dynamo is in 
good order, the engineer or attendant usually cuts out 
all the resistance, and as the generator builds up or, in 
other words, generates current, he proceeds, by the aid 
of the resistance box, to cut down or diminish the flow 
of electricity around the field magnets of the dynamo, 



ELECTRICITY FOR ENGINEERS 67 

and thereby diminish the magnetic density of the 
field magnets and the electromotive force of the 
dynamo. 

We must now gradually turn our rheostat so as to 
cut out resistance and watch the voltmeter, which is 
connected as shown at V in Fig. 20, and receives cur- 
rent whenever the dynamo is operating. Suppose that 
the voltmeter indicates nothing, and we find that the 
dynamo will not generate. On examination of all the 
connections we find everything correct, and we now 
discover that the dynamo field magnets do not contain 
what is termed "residual magnetism" sufficient to start 
the process of generating current. 

Before an armature can generate current it must cut 
lines of force, that is, it must revolve in a magnetic 
field. If the dynamo has been generating current it is 
likely that the iron cores of the field magnets will 
retain sufficient magnetism to start the generation of 
current again. This magnetism which remains in the 
iron is known as residual magnetism. It will make 
itself manifest by attracting the needle of a compass, 
or if strong, a screw driver or a pair of pliers. If we 
find no magnetism in the iron core of the field mag- 
nets, we may take the ends of the shunt winding on the 
field magnets and pass current over them from a bat- 
tery. This current will produce sufficient magnetism 
to cause the generator to build up; in other words, if 
we disconnect these batteries, and connect the wires 
back again from where we got them, we will find that 
we can generate current with the machine. 

When the machine begins to generate, we watch the 
voltmeter and cut resistance in or out of the circuit 
according whether we need to lower or raise the volt- 
age. If we have only one dynamo we may close the 



f>8 ELECTRICITY FOR ENGINEERS 

main switch before we begin generating or after we 
have attained full voltage. 

Again referring to the pole pieces on the dynamo, it 
is possible that there is a sufficient quantity of residual 
magnetism in the pole pieces, and that the polarity of 
both field magnets, between which the armature is 
revolving, is the same. This would also cause the 
dynamo to fail in generating current. If sending bat- 
tery current through the coils does not make one field 
a north pole and the other a south pole, one of the 
fields must be connected wrong, and we must make 
some changes in the connection. 

Referring to Fig. 20, a and b are the terminals of the 
shunt winding on the fields. If the winding of the 
fields is correctly put on it will be as in the little sketch 
at lower corner; that is, if both field magnets were 
taken out of their places and put together, the wind- 
ing should run as one continuous spool. But if the 
winding on one field is wrong, we need simply change 
its connection, as, for instance, transferring c to a and 
a to c. 

In order that a dynamo may excite itself, it is neces- 
sary that the current produced by the residual magnet- 
ism shall flow in such a direction as to strengthen this 
residual magnetism. If the current produced by the 
residual magnetism flows through the field coils in the 
opposite direction this will tend to weaken the residual 
magnetism and consequently to reduce the current 
which flows. 

For this reason if the first attempt to start a dynamo 
with battery current fails, the battery should be applied 
with the opposite poles so that the magnetism it pro- 
duces in the fields will be in the opposite direction. 

The magnetism, the fields, and all parts of the 



ELECTRICITY FOR ENGINEERS 69 

dynamo may be in perfect working order and yet a 
short circuit in any part of the wiring will prevent 
the dynamo from building up This short circuit 
will furnish a path of such low resistance that all cur- 
rent will flow through it and none can flow through the 
fields to induce magnetism. Often dynamos fail to 
generate because of broken wires in the field coils, 
poor contacts at brushes, or loose connections. Some- 
times also part of the wiring may be grounded on 
the metal parts of the dynamo frame. A faulty posi- 
tion of the brushes may also be a cause for the machine 
not generating. In some machines the proper position 
for the brushes is opposite the space between the pole 
pieces, while in other machines their proper position is 
about opposite the middle of the pole piece. If the 
exact position is not known, a movement of the brushes 
will sometimes cause the generator to build up. 

If there are several dynamos to be started great care 
must be taken to see that the second machine is oper- 
ating at full voltage before the switch is closed con- 
necting it to the switch board. The voltage should be 
exactly the same as that of the first machine and the 
rheostat worked to keep it so. If it is less, it is pos- 
sib?e that the first machine will run the second as a 
motor; if it is more, the second machine may run the 
first as motor, the machine having the higher voltage 
will always supply the most current. 

It is also necessary before throwing in the second 
machine (connecting it to the switch board) to see that 
its polarity is the same as that of the machine with 
which it is to run. By reference to Fig. 38 it will be 
seen that the + poles of both machines connect to the 
same bar, and if one of these machines is running and 
we wish to connect the other with it, we must first be 



70 ELECTRICITY FOR ENGINEERS 

sure that the wire of the second machine which leads 
to the top bus-bar is of the same polarity. That is, if 
the top bus-bar is positive, or sends out current, the 
wire or all dynamos connected to it must also be posi- 
tive. The simplest way to find the positive pole of a 
dynamo is with a cup of water. Take two small wires 
and connect one to each of the main wires of the 
dynamo and then insert the bare ends of both wires 
into the water, small bubbles will soon be seen to rise 
in the water from one of the wires. That wire which 
gives off the bubbles is the negative wire. Take care 
that in making this test you do not get the ends of the 
small wires together or against the metal of the cup or 
you will form a short circuit. The polarity of both 
dynamos must be tested and wires of same polarity 
connected to the same bus-bar. 

Where several machines are to be operated in paral- 
lel, compound dynamos are generally used, because it 
is troublesome to keep two shunt machines working in 
harmony. 

The starting of a compound wound dynamo is the 
same as that of a plain shunt dynamo, but in connect- 
ing a compound wound dynamo to its circuit it is 
necessary to be sure that the shunt coils and series coils 
tend to drive the lines of force around the magnetic cir- 
cuit in the same direction. If the series coil is con- 
nected up in the opposite direction to the shunt coil 
the dynamo will build up all right and will work satis- 
factorily on very light loads. When, however, the 
load becomes even, five or ten per cent, of full load, 
the voltage drops off very rapidly and it is impossible 
to get full voltage with even half the load on. This is 
because the ampere turns due to the series coils 
decrease the total ampere turns acting on the magnetic 



ELECTRICITY FOR ENGINEERS 



71 



circuit instead of increasing them as the load comes 
on. This lowers the magnetic flux and of course 
lowers the resulting voltage. In such a case it will be 
necessary to reverse either the field or series coils. 

Fig. 38 and the following description of compound 
dynamos and their connections is taken from Wiring 
Diagrams and Descriptions, by Horstmann and Tousiey, 
published by Frederick J. Drake & Co., Chicago. 




figure 38, 



Fig. 38 shows connections for two compound wound 
dynamos run in parallel. When two or more com- 
pound wound dynamos are to be run together, the 
series fields of all the machines are connected together 
in parallel by means of wire leads or bus-bars which 
connect together the brushes from which the series 
fields are taken. This is known as the equalizer, and 
is shown by the line running to the middle pole of the 
dynamo switch. By tracing out the series circuits it 



72 ELECTRICITY FOR ENGINEERS 

will be seen that the current from the upper brush of 
either dynamo has two paths to its bus-bar. One of 
these leads through its own fields, and the other, by 
means of the equalizer bar, through the fields of the 
other dynamo. So long as both machines are gener- 
ating equally there is no difference of potential between 
the brushes of No. I and No. 2. Should, from any 
cause, the voltage of one machine be lowered, current 
from the other machine would begin to flow through 
its fields and thereby raise the voltage, at the same 
time reducing its own until both are again equal. The 
equalizer may never be called upon to carry much cur- 
rent, but to have the machines regulate closely it 
should be of very low resistance. It may also be run 
as shown by the dotted lines, but this will leave all 
the machines alive when any one is generating. The 
ammeters should be connected as shown. If they 
were on the other side they would come under the 
influence of the equalizing current and would indicate 
wrong, either too high or too low. The equalizer 
should be closed at the same time, or preferably a lit- 
tle before the mains are closed. In some cases the 
middle, or equalizer, blade pf the dynamo switch is 
made longer than the outside to accomplish this. The 
series fields are often regulated by a shunt of variable 
resistance. To insure the best results compound ma- 
chines should be run at just the proper speed, other- 
wise the proportions between the shunt and series coils 
are disturbed. 

GENERAL RULES 

1. Be sure that the speed of the dynamo is right. 

2. Be sure that all the belts are sufficiently tight. 

3. Be sure that all connections are firm and make good contact. 

4. Keep every part of the machine and dynamo room scrupu- 
lously clean. 



ELECTRICITY FOR ENGINEERS 73 

5. Keep all the insulations free from metal dust or gritty sub- 
stances. 

6. Do not allow the insulation of the circuit to become impaired 
in any way. 

7. Keep all bearings of the machine well oiled. 

8. Keep the brushes properly set and see to it that they do not 
cut or scratch the commutator. 

9. If the brushes spark, locate the trouble and rectify it at once. 

10. The durability of the commutator and brushes depends on 
the care exercised by the person in charge of the dynamos. 

11. At intervals the dynamos must be disconnected from the 
circuit and thoroughly tested for leakage and grounds. 

12. In stations running less than twenty-four hours per day, the 
circuit should be thoroughly tested and grounds removed (if any 
are found) before current is turned on. 

13. Before throwing dynamos in circuit with others running in 
multiple, be sure the pressure is the same as that of the circuit; 
then close the switch. 

14. Be sure each dynamo in circuit is so regulated as to have its 
full share of load, and keep it so by use of resistance box. 

15. Keep belting in good order; when several machines are 
operating in parallel and a belt runs off from one, the others will 
run this machine as a motor. 

16. In the same way if you shut down an engine driving a 
generator, the other generators will run the generator and the 
engine. 

Constant Potential Switchboard. In Fig. 39 we show 
the usual type of switchboard employed to connect, 
or switch various dynamos and to feed various circuits 
from. These types, sizes and arrangements of switch- 
boards vary and depend entirely on the type and size 
of the plant, the number of dynamos used and the num- 
ber of circuits to be controlled. The switchboard in 
this cut has three dynamo panels and one load panel. 
At the left of the board and near the top is the volt- 
meter, while on the three left panels are the dynamo 
main switches and their respective amperemeters. On 
the lower part of these three machine panels will be 



74 



ELECTRICITY FOR ENGINEERS 



noticed the protruding hand wheels of the field resist- 
ance boxes, which are hidden back of the board. The 
meter at the top of the right hand panel is the load 
amperemeter and registers the total number of amperes 




*i 


I M 1 


. 0$ ■ 


XL 




Wk 




*k3*rf 


i 




FIGURE 39. 



that are being supplied to the circuits whose several 
switches are just' below the meter. 

Fig. 40 shows diagrammatically the reverse side of a 
similar switchboard. Below all of the switches there 
are installed fuses in each wire. The object of these 
fuses is to protect the wires and also the dynamos. 
These fuses consist of an alloy which melts at a com- 



ELECTRICITY FOR ENGINEERS 



75 



paratively low temperature. If, for instance, a short, 
circuit occurs in any line, the current will suddenly 
become very great and will generate considerable heat. 
This heat will cause the fuse to melt and open the cir- 
cuit. If the fuse did not melt the current would con- 
tinue and overheat the wires, causing considerable 



IO..S O! 

:*■»■ 

■jfj 



E ^ualhie v 



Q Q QT O TX 



Fuses' 



I 



9 9 9 "t~9 9 9 " 9 9 9 




cr 






o 
h 
6 <t 


< 


i 6 






JJJIII 

Switches 

§ 9 r | ? g _? 



FIGURE 40. 



damage and perhaps fires. The fuses should always 
be chosen of such a size that they will melt before the 
current rises enough to do any damage. 

Operation of Constant Current Dynamos. Constant cur- 
rent dynamos differ from constant potential dynamos 
mainly in the higher voltage for which they are usually 



76 ELECTRICITY FOR ENGINEERS 

constructed. Such machines are always more or less 
dangerous to life, and great care must be taken not to 
touch any of the current-carrying parts with bare hands. 

When such parts must be handled rubber gloves are 
very convenient and useful if kept dry. High voltage 
machines should always be surrounded by insulating 
platforms of dry wood, or rubber mats, so arranged 
that one must stand on them in order to touch any 
part of the machine. By reference to Fig. 19 it will 
be seen that the constant current dynamo is not 
equipped either with a voltmeter or a field rheostat; 
but an amperemeter should always be used. The 
troubles encountered with these dynamos are much the 
same as those of constant potential dynamos. Most of 
them are referred to in the following descriptions and 
instructions for different systems and to avoid repeti- 
tion need not be mentioned here. 

The type of dynamo generally used with constant 
currents is shown in Fig. 19 and is series wound; that 
is, the same current that passes through the lights also 
passes through the fields and excites them. The fields 
of this dynamo are connected with a short circuiting 
switch, S, which is generally used when the machine is 
to be shut down. When this switch is closed it forms 
a path of much lower resistance than do the fields of 
the dynamo and all current passing through it and the 
dynamo loses its magnetism and stops generating. 
A constant potential dynamo will not begin genera- 
ting if there is a short circuit anywhere in the wiring 
connected with it, but with the constant current 
dynamo it is often necessary to provide a short circuit 
in order to start it. If there is very much resistance 
in the line or if it is entirely open the dynamo will fail 
to generate. 



ELECTRICITY FOR ENGINEERS 77 

. In order to start generation a small wire may be 
attached to one of the terminals of the dynamo and 
the other end brought in contact with the other ter- 
minal for a fraction of a second or the shortest possible 
instant. If the circuit happens to be arranged some- 
what as shown in the figure, the plug may be inserted 
so that ihe dynamo is started through only one lamp. 
When this lamp is burning properly the plugs may be 
suddenly withdrawn and the current will now force 
itself through the other lamps. This process is known 
as "jumping in" and should be used only in an emer- 
gency, as much damage may be caused, especially if a 
dynamo is already running a large number of lamps 
and is then "jumped into" a bad circuit. This is also 
often done, but is just as dangerous as it would be to 
attempt to start a heavy steam engine by opening up 
the throttle valve with a quick jerk. 

Constant current dynamos are always equipped with 
automatic regulators and before the dynamo is started 
special attention must be given the regulator to see 
that it is in proper working order. 

Often it may be desirable and even necessary to run 
two dynamos in series, as, for instance, if a circuit has 
been extended beyond the capacity of -one machine. 
In such a case the regulator of one machine is cut out 
and that machine set to operate at about its highest 
electromotive force, and, the variations are taken care 
of by the other dynamo. 

The Brush System. The brush arc dynamo is quite 
distinct from other constant current dynamos in general 
use. We shall therefore give the following descrip- 
tion of it taken from literature furnished by the Gen- 
eral Electric Company. 

The brush arc generator is of the open coil type, the 



78 ELECTRICITY FOR ENGINEERS 

fundamental principle of which is illustrated in Fig. 
41. Two pairs of coils, placed at right angles on an 
iron core, are rotated in a magnetic field. The hori- 
zontal coils represented in the diagram are producing 
their maximum electromotive force, while the pair of 
coils at right angles to them is generating practically 
no electromotive force. The brushes are placed on 
the segments of the four-part commutator, so as to col- 
lect only the current generated by the two horizontal 




FIGURE 41. 

coils. The other coils are open circuited or com- 
pletely cut out of the circuit. 

Such a machine will generate current, continuous in 
direction, but fluctuating considerably in amount. 
These fluctuations will be diminished by the addition 
of more coils to the armature. 

Fig. 42 shows the connections of an eight-coil brush 
arc generator. Each bobbin is connected in series 
with the one diametrically opposite. The connection 
is not shown on the diagram. It will be noticed that 
of those coils connected to the outer ring on which the 
brushes A and A 1 bear, only 3, 3 1 are in circuit, 1, I 1 






ELECTRICITY FOR ENGINEERS 



79 



being entirely cut out; while on the inside ring all 
coils 2, 2 1 and 4, 4 1 are in circuit, the two pairs being 
parallel; 4, 4 1 are coming into the field of best action; 
in other words, they are approaching that part of the 
field in which there is most rapid change of magnetic 
flux, while 2, 2 1 are approaching that part in which the 
flux is uniform. In 4, 4 1 there is an increasing electro- 




figure 42. 

motive force being generated, and the current is rising; 
while in 2, 2 1 , the electromotive force is decreasing and 
the current falling. Unless 2, 2 1 were cut out of the 
circuit, a point would soon be reached where the elec- 
tromotive force in 2, 2 1 would be zero, and conse- 
quently 4, 4 1 would be short circuited through 2, 2 1 . 
Just before this occurs, however, 2, 2 1 have passed from 
under the brush and the small current still flowing 



80 ELECTRICITY FOR ENGINEERS 

draws out the spark one sees on the commutator of all 
open coil machines. 

Setting the Brushes. A pressure brush should always 
be used over the under brush in the same holder, as it 
improves the running of the commutator and secures 
better contact on the segment. The combination is 
referred to as the "brush." The brushes should be 
set about 5^3 in. from the front side of the brass brush- 
holder. 

In setting the brushes, commence with the inner pair 
and set one brush about 5^3 in. from the holder to tip 
of the brush, then rotate the rocker or armature until 



figure 43. 

the tip of the brush is exactly in line with the end of a 
copper segment, as shown in Fig. 43. The other 
brush should be set on the corresponding segment 90 
removed (the same relative position on the next for- 
ward segment); but if the length of the brush from the 
holder is less than $}i in., move both brushes forward 
until the length of the shorter brush from the holder 
is 5^ in. Now set the two extreme outer brushes in 
the same manner, clamping firmly in position, and by 
using a straight edge or steel rule, all the brushes can 
be set in exactly the same line and firmly secured. 
The spark on one of the six brushes may be a trifle 



ELECTRICITY FOR ENGINEERS 81 

longer than on the others. In this case, move the 
brush forward a trifle so as to make the sparks on the 
six brushes about the same length. Equality in 
the spark lengths is not essential, but it gives at a 
glance an indication of the running condition of the 
machine. 

Brushes should not bear on the commutator less than 
}i in. from the point of the brush, or, as illustrated in 
Fig. 44 (a), they will tend to drop into the commu- 
tator slots and pound the copper tip of the wood block, 
causing the fingers of the brushes to break off. If, on 
the other hand, the bearing is too far from the end, or 
the brushes are set too long, as in Fig. 44 (b), the 



figure 44a. figure 44b. figure 44c. 

point of the brush will not be in contact with the seg- 
ment, thereby prolonging the break, and allowing the 
spark to follow the tip with consequent burning of the 
segments and brushes. 

Fig. 44 (c) shows correct seating with the tip of the 
brush nearly tangential and stiff on the segment as it 
leaves. 

Care of Commutator. If the commutator needs lub- 
rication, oil it very sparingly. Once or twice during 
a run is ample. If the oil has a tendency to blacken 
the commutator instead of making it bright, wipe the 
commutator with a dry cloth. Too much oil causes 
flashing. 

The machine, of course, generates high potential, 
and the cloth, or whatever is used to oil the commu- 



82 ELECTRICITY FOR ENGINEERS 

tator, should therefore be placed on a stick so that the 
hand is not placed in any way between the brushes. 

A rubber mat should be provided for the attendant 
to stand on when working around the commutator or 
brushes. 

One hand only should be used, and great care exer- 
cised not to touch two brush clamps or brushes at the 
same time; never with switches closed. 

As soon as current is shut off from the machine the 
commutator should be cleaned. A piece of very fine 
sandpaper held against the commutator under a strip 
of wood for about a minute before the machine is 
stopped, will scour the commutator sufficiently. The 
brushes need not be removed. An effort should be 
made to have the machine cleaned immediately after 
it is shut down. Five minutes at that time will give 
better results than half an hour when the machine is 
cold. Never use a file, emery cloth or crocus, on the 
commutator. New blocks will sometimes cause flash- 
ing, due to the presence of sap in the wood. The 
machine should be run for a few hours with a slightly 
longer spark, say y 2 in., and the commutator then 
thoroughly cleaned with fine sandpaper. 

All constant current arc machines require an auto- 
matic regulator to increase the voltage as more lamps 
are cut into the circuit and decrease it as lamps are 
cut out. 

We will give only one of the several forms of regu- 
lators used with this system. 

The form I regulator is placed on the frame of the . 
machine beneath the commutator, and a constant 
motion is imparted to its main shaft through a small 
belt running around the armature shaft. (See Fig. 
46.) By means of magnetic clutches and bevel gears, 



ELECTRICITY FOR ENGINEERS 83 

a pinion shaft is rotated, which moves the rack and the 
rocker arm and so shifts the brushes on the commu- 
tator to maintain a spark of about $/% in. on short cir- 




To Controller 



\ To Controller 



FIGURE 46. 



cuit and }i in. at full load; at the same time the 
rheostat arm is moved over the contacts to cut 
resistance in or out of the shunt around the field 
circuit. 



84 



ELECTRICITY FOR ENGINEERS 



The current for the magnetic clutches is regulated by 
the controller. 

The controller consists principally of two magnets 
which are energized by the main current and act when 
the current is too high or too low by sending a small 
current to one of the clutches. 

A careful examination of the controller (see Fig. 
47), in connection with Fig. 46, will give a clear idea 



CONNECTIONS OF BRUSH CONTROLLER 

To Held &\ Ar-vT) /^ To Circuit or Ammeter 



HI! (T-j-^P r ' y i_j_- r U 




Changed S June's 



FIGURE 47. 



of its regulating action. It is generally advantageous 
to make the yoke which carries the brushes on the 
machine and the arm moving the rheostat, rather 
tight. As the magnetic clutches act with considerable 
force, it is not necessary to adjust these moving parts 
so loosely that they will move without considerable 
pressure on the rocker handle. Less difficulty will 
then be experienced in adjusting the controller. 



ELECTRICITY FOR ENGINEERS 85 

For shunt lamps, the controller may be adjusted to 
permit a variation of .4 ampere above or below normal; 
for differential lamps, the variation above and below 
normal should not exceed .2 ampere. The limits 
given in the following instructions are for differential 
lamps, and may be extended .2 ampere above or below 
for shunt lamps. 

If the controller is out of adjustment and fails to 
keep the current normal, do not try to adjust the ten- 
ions of both armatures at the same time. For exam- 
ple, suppose the current is too high, either one of the 
two spools may be out of adjustment. The left-hand 
spool I may not take hold quickly enough, or the 
spool F may take hold too quickly. To make the 
adjustment, screw up the adjusting button K on the 
right hand spool, increasing the tension. This will 
have a tendency to let the current fall much lower 
before the armature comes in contact with H, to cause 
the current to increase. By simply tapping the arma- 
ture G quickly with a pencil or piece of wood, forcing 
it down to its contact, and at the same time watching 
the ammeter, the current may be brought up to 6.8 
amperes if 6.6 amperes is normal, or to 9.8 if 9.6 
amperes is normal. With the current at 6.8 amperes, 
which is .2 ampere high, the adjusting button L should 
be turned. to increase the tension on this spring until 
the armature M comes in contact with contact N, 
which will force current down through O. The clutch 
which pulls the brushes forward and rocks the rheostat 
back for less current will thus be energized. Repeat 
this adjustment two or three times, but do not touch 
the adjusting button K; adjust L until it is just right. 

At the side of the armature M a little wedge is 
screwed in by means of an adjusting button, and 



80 ELECTRICITY FOR ENGINEERS 

increases or decreases the leverage on this armature. 
See that this wedge is fairly well in between the core 
or frame of the spool and the spring of the armature. 
The armature M may have to be taken out and the 
spring slightly bent. It is advisable to have the screw 
which passes through the adjuster button L about half 
way in, to allow an equal distance up and down for 
adjusting this lighter spring after the wedge shaped 
piece is in the right position to give the necessary 
tension on the spring which is fastened to the arma- 
ture M. 

In the right-hand corner P, a small bent piece of 
wire is placed for tightening up the screw which fas- 
tens the spring to the frame of the spool. As the con- 
tact made by the spring and the frame of the spool 
held together by a screw and button is a part of the 
magnetic circuit, it will be almost impossible to get 
this spring back to exactly the same tension after once 
removing it. Therefore, the adjusting buttons of the 
controller must be turned slightly in order to bring it 
back to its proper adjustment. This, however, is an 
after consideration, and care should be taken to have 
the screw which holds the spring and frame together 
always tight. 

Having adjusted the spool I so that the current will 
not rise above 6.8 amperes (or 9.8 amperes), move the 
armature M up to contact N with a pencil or piece of 
wood, causing the current to be reduced to about 6.2 
(or 9.2). After the current settles at this point, decrease 
the tension on the spring which is fastened to armature 
G, allowing this armature to fall down to contact H. 
Current will then flow through Q, which will rock the 
brushes back and also move the rheostat arm for more 
current. As the spool I has been adjusted for 6.8 (or 



ELECTRICITY FOR ENGINEERS 87 

9.8) amperes, the current cannot rise above that amount 
no matter how the spool F is adjusted. 

With very little practice in moving the armature of 
one spool with a pencil, the other can be adjusted 
much more readily than if an attempt is made to adjust 
the screws K and L at the same time. 

The two small shunt coils, R and S, are connected 
around the two contacts simply to decrease the spark 
between the silver and platinum contacts. If they 
should" become short circuited in any way, so that 
their resistances become diminished, sufficient current 
may pass through either of them to operate the regu- 
lator. If unable to locate the trouble disconnect these 
coils at points T and U, when a thorough examination 
can be made. M and G need not move more than just 
enough to open the contact; ^ m - ls ample. 

In starting the machine, the lower switch, which 
short circuits the field, should be opened last. 

The switch in the left-hand corner of the controller, 
figure 47 cuts out the two resistance wires which are 
used to force the current through wires O and Q to 
the clutches. Open this switch, which leaves the 
automatic device of the controller in circuit, so that it 
will move the brush rocker. Unclamp the brush rocker 
from the rheostat arm rocker. Move the brushes by 
hand to give the proper spark, allowing the rheostat 
arm, however, to be moved by the controller. After 
the switches are opened, the rheostat arm will go clear 
around to a full load position, and then, as the current 
rises, the controller takes hold and brings the arm 
back. In the meantime, rock the brushes forward or 
backward and keep the spark about the proper length, 
say }& in., at full load to ^ in., on short circuit. 
Gradually the rheostat arm will settle, the spark will 



88 



ELECTRICITY FOR ENGINEERS 



become constant, and the machine will give its proper 
current. Then clamp the rocker and rheostat- arm 
together and let the machine regulate itself. 

This method is much better than opening the 
switches on the machine and allowing the wall con- 
troller to take care of the machine from the start. By 
allowing the controller to start the machine, a trifle 
longer spark is obtained than by the other method, 



PULLEY END 



COMMUTATOR END 




figure 48. 



unless the machine is run from the beginning on a very 
full load. 

The machine will require a trifle longer spark on 
light load, or on bad circuits, than when running at 
full load. This fact should be borne in mind in wet 
weather, when trouble with grounds is experienced. 

A reliable ammeter should always be connected in 
the circuit of an arc generator, so that the exact cur- 
rent may be read at a glance. It should be connected 
into the negative side of the line where the circuit 
leaves the regulator. 



ELECTRICITY FOR ENGINEERS 



89 



The Thomson-Houston System. The Thomson-Hous- 
ton dynamo differs from other arc dynamos principally 
in the nature of its armature winding. This is shown 
in Fig. 48. One end of each of the three coils is con- 
nected to a copper ring common to all. The other end 
of each coil terminates at one of the three commutator 
segments. The management and operation of the 
machine will appear from the following instructions 
taken from pamphlets furnished by the General Elec- 
tric Company. 




FIGURE 50. 

Setting the Cut-out. After the brushes are in position 
the cut-out must be set. This is done by turning the 
commutator on the shaft in the direction of rotation 
(if the commutator is set in position the whole arma- 
ture must be revolved) until any two segments are just 
touching the primary brush on that side, as segments A' 
and A'" touch brush B 4 in Fig. 50. 

Under these conditions brush B 1 should be at the 
left-hand edge of upper segment. Then turn commu- 
tator until the same two segments are just touching 



90 ELECTRICITY FOR ENGINEERS 

brush B 2 , when the end of brush B 3 should just come 
to the right-hand edge of the lower segment. If the 
secondary brush projects beyond the edge of the seg- 
ment the regulator arm should be bent down; if it does 
not come to the edge of the segment, the arm should 
be bent up. 

Care must be taken that the regulator armature is 
down on the stop when the cut-out is being set. 
These adjustments by bending regulator arm are 
always made in the factory before testing the machine, 
and should never be made on machines away from the 
factory, unless the regulator arm has been bent by 
accident. If it becomes necessary to make any adjust- 
ments they should be made by means of the sliding 
connection attached to the inner yoke. 

Always try the cut-out on both primary brushes. If 
it does not come the same on both, turn one over. If 
the brush-holders are correctly set by the gauge, there 
should be no trouble in getting the cut-out set properly 
after one or two trials. 

To set the commutator in the proper position on a 
right-hand machine, with a ring armature, find the 
leading wire of No. I coil. It is the custom in the 
factory to paint this lead red, also to paint a red mark 
on the center band between two groups of coils, 
namely, the last half of No. I coil and the first half of 
No. 3 coil. The first half of a coil is that group from 
which the lead comes. The last half is diametrically 
opposite the first half and the lead wire belonging to 
it is- connected with the brass ring on the outside of 
the connection disk on the commutator end. 

In Fig. 51 the first halves of the. three coils are rep- 
resented by 1, 2 and 3, and the last halves by i', 2' 
and 3', 



ELECTRICITY FOR ENGINEERS 9; 

A narrow piece of tin with sharply pointed ends is 
bent up over the sides of the middle band at the cen- 
ter of the red mark so that the points are opposite each 
other. 

When the red mark and red lead have been found, 
turn the armature until the last half of No. I coil has 
wholly disappeared under the left field and until the 
left-hand edge of the first coil to the right of the red 




FIGURE 51. 



mark (No. 3 in Fig. 51) is just in line with the edge of 
the left field. The red lead will then be in position 
shown in Fig 51, and the armature is in proper posi- 
tion to set the commutator. 

In the case of the right-hand drum armature 'he 
leading wire of the first coil should be found. This lead 
may be recognized from the fact that it is more heavily 
insulated than the rest, and is found in the center of 



92 



ELECTRICITY FOR ENGINEERS 




FIGURE 52. 



the outer coil, on the commutator end. With this 
wire turned underneath, rotate the armature forward, 
or counter-clockwise, until the pegs on the right-hand 




Red mark painted 
on center band. 



FIGURE 53. 



ELECTRICITY FOR ENGINEERS 



93 



side of this coil just disappear under the left field. 
(See Fig. 52.) 

The position of the red lead and the red mark on the 
band are the same on all armatunes, but their positions 
in the fields of the machines called left-hand (clock- 
wise rotation), should be as shown in Fig. 53 and 54 
when setting the commutator. 

When the armature of a right-hand machine is in 
position, the commutator is turned on the shaft until 




figure 54. 



segment No. 1 is in the same relative position as the 
last half of No. 1 coil; segment No. 2 should corres- 
pond with the last half of No. 2 coil, and segment No. 
3 with the last half of No. 3 coil, as shown on Figs. 51 
and 52. 

For left-hand machines, see Figs. 53 and 54. 

The distance from the tip of the brush, which is on 
top, to the left-hand edge of No. 2 segment on a right- 
hand machine, or to the right-hand edge of No. 3 seg- 



f)4 ELECTRICITY FOR ENGINEERS 

ment in a left-hand machine is called the lead, and 
should be made to correspond with the following 
table. 

TABLE OF LEADS 
DRUM ARMATURES. RING ARMATURES. 

C 12 \ inch positive K 12 ^g inch positive 

E 12 / F " " M 12 i " negative 

E 2 J «' « M 2 I " 

H 12 4 " " LD 12 \ " positive 

H 2 J « « . LD* i " 

MDi 2 ^| " 

MD 2 if •< 

Place the screws in the binding posts at the lower 
ends of the sliding connections, and put on the dash 
pot connections between the brushes, with the heads 
of the connecting screws outward. In every case the 
barrel part of the dash pot is connected to the top 
brush-holder, and plunger part to the bottom brush- 
holder. 

See that the field and regulator wires are connected 
and that all connections are securely made. 

When all connections have been made, make a care- 
ful examination of screws, joints and all moving parts. 
They must be free from stickiness and not bind in any 
position. 

To determine when the machine is under full load, 
notice the position of the regulator armature, which 
should be within }i in. of the stop. At full load the 
normal length of the spark on the commutator should 
be about T 3 g in. If it is less than this, shut' down the 
machine and move the commutator forward or in the 
direction of rotation until the spark is of the desired 
length. If the spark is too long, move the commu- 
tator back the proper amount. 

A general view of the complete dynamo is given in 



ELECTRICITY FOR ENGINEERS 



95 



Fig. 55, and will help explain the regulator used with 
this system. 

The regulator is fastened to the frame of the machine 
by two short bolts. On the right»hand machine its 
position is on the left-hand side, as shown in Fig. 55. 
On the left-hand machine, i.e., one which runs clock- 
wise, its position is on the opposite side. Before fill- 




FIGURE 55. 



ing the dash pot D with glycerme, see that the 
regulator lever and its connections, brush yokes, etc., 
are free in every joint, and that the lever L can move 
freely up and down. Then fill the -dash pot D with 
concentrated glycerine. The long wire from the 
regulator magnet M is connected with the left-hand 
binding post P of the machine, and the short wire with 



96 



ELECTRICITY FOR ENGINEERS 



the post P 2 on the side of the machine. The inside 
wire of the field magnet, or that leaving the iron flange, 
of the left-hand field should be connected into post P 2 
also, as shown in Fig. 55. The electric circuit (see 
Fig. 56) should be complete from post P l , on the con- 
troller magnet, through the lamps to the post N on the 
machine, through the right-hand field magnet C, to 
the brushes B 1 B 1 , through the commutator and arma- 
ture to the brushes B B, through the left-hand field C, 




IGURE 56. 



to posts P 2 and P, thence to posts P 2 and P on the con- 
troller magnet, through the controller magnet to P 1 . 
The current passes in the direction indicated by the 
arrows 

When an arc machine is to be run frequently at a 
small fraction of its normal capacity, the use of a light 
load device is advisable to secure the best results in 
regulation. 

The rheostat for this purpose (see Fig. 57) is con- 
nected in shunt with the right field of the generator. 



ELECTRICITY FOR ENGINEERS 97 

Facing the rheostat with the right binding posts at the 
bottom, the contact on the right side or No. I gives 
open circuit and throws the rheostat out of use. Point 
No. 2 gives a resistance of 44 to 46 ohms and Point 
No. 3 gives a resistance of 20 to 22 ohms. 

This rheostat with a 75-light machine allows the fol- 
lowing variations: Point 1, 75 to 48 lights; Point 2, 
48 to 25 lights; Point 3, 25 lights or less. For use with 




FIGURE 57. 



other sizes of generators, the adjustment of the rheo- 
stat must be made to suit the conditions. 

When the rheostat is in use, the sparks at the com- 
mutator will be somewhat larger than normal, but will 
not be detrimental. 

The controller magnet (see Fig. 58) is to be fastened 
securely by screws to the wall or some rigid upright 
support, taking care to have it perfectly plumb. It is 
connected to the machine in the manner shown in Fig. 
55, i.e., the binding post P 2 on the controller magnet is 



98 



ELECTRICITY FOR ENGINEERS 



connected to the binding post P 2 (see Fig. 55) on the 
end of the machine, and likewise the post P on the 
controller to the post P on the leg of the machine; 
the post P 1 forms the positive terminal from which the 
circuit is run to the lamps and back to N. 

Great care should be taken to see that the wires P P 




FIGURE 58. 



and P 2 P 2 are fastened securely in place; for if connec- 
tion between P and P should be impaired or broken, 
the regulator magnet M would be thrown out of action, 
thus throwing on the full power of the machine, and if 
the wire P 2 P 2 should become loosened, the full power 
of the magnet M would be thrown on, and the regu- 



ELECTRICITY FOR ENGINEERS 99 

lator lever L, rising in consequence, would greatlj- 
weaken or put out the lights. 

The wires leading from the controller magnet to the 
machine should have an extra heavy insulation. 

Care should be taken in putting up the controller 
magnet that the following directions are followed: 

1. The cores B of the axial magnets CC must hang 
exactly in the center, and be free to move up and 
down. 

2. The screws fastening the yoke or tie pieces to the 
two cores must not be loosened. 

3. The contacts O must be firmly closed when the 
cores are not attracted by the coils C C, which is the 
case, of course, when no current is being generated by 
the machine, and when the cores are lifted, the con- 
tacts must open from g- 1 ^ in. to ^ in.; a greater open- 
ing than ^ in. has the effect of lengthening the time 
of action of the regulator magnet. This tends to ren- 
der the current unsteady, and in case of a very weak 
dash pot or short circuit might cause flashing. Adjust- 
ment must be made if necessary by bending the lower 
contact up or down, taking care that it is kept parallel 
with the upper contact, so that when they are closed, 
contact will be made across its whole width. If this 
adjustment is not properly made there will be destruc- 
tive sparking on a small portion of the contact surfaces. 

4. All connections must be perfectly secure. 

5. The check nuts N must be tight. 

. 6. The carbons in the tubes L must be whole. These 
carbons form a permanent shunt of high resistance 
around the regulator magnet M, and if broken will 
cause destructive sparking at contacts O, burning them 
and seriously interfering with close regulation of the 
generator. In case a carbon should become broken, 



100 ELECTRICITY FOR ENGINEERS 

temporary repairs may be made by splicing the broken 
pieces with a fine copper wire. 

To keep the action of the controller perfect the con- 
tacts O should be occasionally cleaned by inserting a 
folded piece of fine emery cloth and drawing it back 
and forth. 

The amount of current generated by each machine 




FIGURE 59. 

depends upon the adjustment of the spring S. If the 
tension of this spring is increased the current will be 
diminished; if the tension is diminished, the current 
will be increased. 

In starting these dynamos when the armature has 
reached its proper speed, the short circuiting switch on 
the frame should be opened. This method allows the 



ELECTRICITY FOR ENGINEERS 



101 



generator to take up its load gradually, and is a very 
important point in the handling of the machine. 

Arc Switchboards. Fig. 59 shows a general view of 
the Thomson-Houston plug switchboard. A rear view 
of the same board is given in Fig. 60. 

In a standard panel the number of horizontal rows 
of holes equals one more than the number of gener- 
ators. The vertical holes are always twice the number 
of generators. The positive leads of the generators are 




FIGURE 60. 



attached to the binding posts on the left-hand ends of 
the horizontal conductors. The negative leads are 
connected to the corresponding binding posts at the 
right-hand end of the board. 

The positive line wires are connected to the vertical 
straps on the left, and the negative wires to the similar 
straps on the right of the center panel. 

If a switchboard plug be inserted in any of the holes 
of the board, it puts the corresponding generator lead 



102 ELECTRICITY FOR ENGINEERS 

and the line wire in electrical connection, but as the 
positive line wires are back of the positive generator 
leads only, it is not possible to reverse the connection 
of the line and the generator accidentally, though any 
other combinations of lines and generators can be 
made readily and quickly. 

The holes of the lower horizontal rows have bushings 
connected with the vertical straps only. Plugs con- 
nected in pairs by flexible cable and inserted in the 
holes put the corresponding vertical straps in connec- 
tion as needed, and normally independent lines may be 
connected when one generator is required to supply 
several circuits. 

Lines and generator leads may be transferred, while 
running, by the use of these cables, without shutting 
down machines or extinguishing lamps. 

The standard boards are arranged for an equal num- 
ber of generators and circuits, but special boards for 
any ratio of circuits to generators can be built. 

As it is sometimes convenient, even in small plants, 
to interchange lines and generators without shutting 
down machines, a special transfer cable with plugs has 
been devised. This serves the same purpose as the 
regular transfer cable, but the plugs may be used in 
any of the holes of the switchboard, as they are insu- 
lated, except at the tip, and when inserted connect 
with the line strips only. 

The transfer of circuits from one generator to 
another gives trouble to dynamo tenders who are not 
familiar with the operation of these plug switchboards. 
Fig. 61 illustrates the successive steps for transferring 
the lamps of two independent circuits from two genera- 
tors to one without extinguishing the lamps on either 
circuit. 



ELECTRICITY FOR ENGINEERS 



103 



4- 


12 3 4 


12 3 4 




1 , ' 


-•(boo • — vO/— e — ©■ 


1 , 1 


1 2 

3 


(J • LJ LJ u • u u 
OOOO OOOO 
OOOO OOOO 


2 1 

3 



♦ — # 



o o 
o o 

OOOO 
OOOO 



rt 



OOOO 
OOOO 



^1 

3 





1 






c 






1 










?/■ 


-H 


i> o. 


o 


4- 


-y>r 




r\ 




1 1 


\J 


<J 


1 1 


1 


i 


C 


) o 


o 


o 


1 






1 


1 2 


^ 


•^ 


u 


L> 


2 1 


. 1 

3 





C 


) o 


o 


o 


o 


o 


o 


1 
3 




o 


C 


2) O 


o 


o 


o 


o 


o 






FIGURE 61. 



104 ELECTRICITY FOR ENGINEERS 

This process is a very simple example of switch- 
board manipulation, but illustrates the method used 
for all combinations. 

The location of plugs is shown by the black circles, 
which indicate that the corresponding bars of the 
horizontal and vertical rows are connected. 

Circuit No. I and No. 2, running independently from 
generators No. 1 and No. 2 respectively, are to be 
transferred to run in series on generator No. 2. 

In A, Fig. 61, are two circuits running independently; 
in B the positive sides of both generators and circuits 
are connected by the insertion of additional plugs. 

At C both generators and circuits are in series. 

Next insert plugs and cables as shown in D. Then 
withdraw plugs on row corresponding to generator No. 
1, and the circuits No. 1 and No. 2 are in series on 
machine No. 2, and machine No. 1 is disconnected as 
at E. ■ • 

Similar transfers can be made between any two cir- 
cuits or machines, and by a continuation of the process 
additional circuits can be thrown in the same machine. 
The transfer of the two circuits to independent genera- 
tors is accomplished by reversing the process illus- 
trated. 

Fig. 62 shows the wiring and connections of the 
Western Electric Co.'s series arc switchboard. At the 
top of the board are mounted six ammeters, one being 
connected in the circuit of each machine. On the 
lower part of the board are a number of holes, under 
which, on the back of the board, are mounted spring 
jacks to which the circuit and machine terminals are 
connected. For making connections between dynamos 
and circuits, flexible cables terminating at each end in 
a plug, are used; these are commonly called "jump- 



ELECTRICITY FOR ENGINEERS 



105 



ers." The board shown has a capacity of six machines 
and nine circuits, and with the connections as shown 
machine I is furnishing current to circuit I, machine 2 
is furnishing current to circuits 2 and 3, and machine 4 
is furnishing current to circuits 4, 5 and 7. In con- 
necting together arc dynamos and circuits the positive 
of the machine (or that terminal from which the cur- 
rent is flowing) is connected to the positive of the cir- 




FIGURE 62. 



cuit (the terminal into which the current is flowing). 
Likewise the negative of the machine is connected to 
the negative of the circuit. Where more than one cir- 
cuit is to be operated from one dynamo, the - of the 
first circuit is connected to the + of the second. At 
each side of the name plate (at 3, for instance) there 
are three holes. The large hole is used for the per- 
manent connection, while the smaller holes are used 
for transferring circuits, without shutting down the 



100 ELECTRICITY FOR ENGINEERS 

dynamo. Smaller cables and plugs are used for 
transferring. If it is desired to cut off circuit 5 from 
machine 4, a plug is inserted in one of the small holes 
at the right of 4, the other plug being inserted in one 
of the holes at the left of 7. Circuit 5 would now be 
short circuited, and the plug in the + of 5 can now be 
transferred to the permanent connection in the + of 7, 
and the cords running to 5 removed. If it is desired 
to cut in a circuit, say circuit 6 onto machine 2, insert a 
cord between the — of circuit 2 and the -f-of 6 and an- 
other between the — of 6 and the + of 3. Now pull the 
plug on the cord connecting — of 2 and the + of 3 and 
insert the permanent connections. In cutting in cir- 
cuits, if they contain a great number of lights, a long 
arc may be drawn when the plug between 2 and 3 is 
pulled, and it is sometimes advisable to shut down the 
machine when making a change of this kind. 



CHAPTER V 

MOTORS. — ALTERNATING CURRENT MOTORS. 

Motors. Any dynamo may be used as a motor and con- 
sequently we have as many types of motors as there are 
types of dynamos. The pull of a motor depends upon 
the repulsion and attraction between the lines of force, 
or magnetism of the wire and core of the armature and 
that of the fields. We have seen that in a dynamo, as 
we force a wire through a magnetic field, current is 
generated. The more current there is generated or 
flowing in such a wire, the greater will be the expendi- 
ture of power necessary to force such a wire through a 
magnetic field; in other words, the currents flowing in 
the wires of a dynamo armature, always tend to drive 
the armature in a direction opposite to that in which it 
is being driven. 

If, then, instead of revolving a dynamo armature by 
mechanical means, we connect it to a source of elec- 
tricity and allow a current to flow through it we must 
obtain motion, and the direction of this motion will 
depend upon the direction in which the current flows, 
so long as this current does not alter the magnetism of 
the fields. 

We have already seen that the electric motor is built 
exactly like a dynamo; consequently, as its armature 
revolves it not only does useful work, such as turning 
whatever machinery it is belted to, but it also gener- 
ates an electromotive force. For instance, if a motor, 
running at full speed and receiving current from a 
107 



108 ELECTRICITY FOR ENGINEERS 

dynamo (Fig. 63), were suddenly disconnected by 
opening the main switch, it would at once begin acting 
as a generator and sending out current. This can be 
easily seen with any motor equipped with a starting 
box, such as shown; for the current from the motor 
will continue to energize the fields and the little mag- 
net M so as to hold the arm of the starting box until 
the motor has nearly come to rest. If it were not for 
the current generated by the motor, this arm would fly 
back the instant the switch is opened. 

The electromotive force set up by a motor always 
opposes that of the dynamo driving it; that is, the 
current which the motor tends to send out would flow 
in the opposite direction to that which is driving it. 

This may be compared, and is somewhat similar, to 
the back pressure of the water which a pump is forcing 
into a tank. If the check valves were removed and 
the steam pressure shut off, the water would tend to 
force the pump backward. 

This electromotive force is called the counter elec- 
tromotive force of the motor. The counter electro- 
motive force of the motor varies with the speed of the 
motor and also limits the speed of the motor, for it is 
obviously impossible that a motor should develop 
higher counter E. M. F. than the E. M. F. of the 
dynamo driving it. 

This highest possible speed of a motor is, then, that 
speed at which its counter E. M. F. becomes equal to 
the E. M. F. of the dynamo supplying the current, and 
this is the speed which would be obtained were the 
motor doing no work and running without friction. 
This condition is impossible in practice, and the 
counter E. M. F. of the motor is always less than the 
E. M. F. of the dynamo. In order to speed up a 



ELECTRICITY FOR ENGINEERS 109 

motor we must arrange it so that it must run faster in 
order to develop an E. M. F. equal to that of the 
dynamo; we can do this by lessening the number of 
turns of wire on the armature, or by lessening the 
magnetism of the fields. In doing so, however, we 
also lessen the capacity of the motor for performing 
work. 

The power that can be obtained from an electric 
motor depends upon two things: the current flowing in 
its armature coils and the strength of magnetism devel- 
oped in the fields. 

Assuming the fields as remaining constant, the power 
of the motor must then vary as the current flowing 
through it. Suppose we have a motor being driven by 
an E. M. F. of no volts and it is doing no work; it 
will be running at full speed and its counter E. M. F. 
will therefore also be very near no volts. If now a 
load be thrown on this motor, it must get more current 
.in order to develop the necessary power to carry the 
load. 

Throwing on the load will decrease the speed of this 
motor, and consequently its counter E. M. F. will fall, 
say to ioo volts. The E. M. F. of the dynamo being 
no and the counter E. M. F of the motor ioo, there 
will be considerable current forced through the arma- 
ture of the motor, so that it can now handle the load. 

The current in the armature at all times will equal 

E - E' 

— ~ — where E is the electromotive force of the 
K 

dynamo, E' the counter electromotive force of motor, 

and R the resistance of the motor armature. In order 

that a motor should keep a nearly uniform speed, for 

varying loads, the resistance of its armature should be 

very low, for then a slight drop in counter E. M. F 



no 



ELECTRICITY FOR ENGINEERS 



will allow considerable current to flow through the 
armature. The above applies particularly to the shunt 
motor shown in Fig. 63. In this diagram C is a double 
pole fuse block, S the main controlling switch, R the 
starting box, or rheostat, M the magnet, which holds 
the arm of the starting box in place when it is broughc 




figure 63. 



over against it, F the fields, and A the armature of the 
motor. 

The current enters, say at the right hand fuse, and 
passes to the starting box and along the fine wires 
shown in dotted lines through the fields of the motor 
and coil M to the other fuse. The fields of the motor 
and the little magnet M are now charged, but as yet 



ELECTRICITY FOR ENGINEERS 111 

there is no current passing through the armature and 
no motion. We now slowly move the arm on the start- 
ing box to the right; this admits a little current, 
limited by the resistance in the starting box, to the 
motor armature and it begins to revolve, and as we 
continue to move the arm to the right, the armature 
gains in speed because we admit more current to it by 
cutting out more and more resistance. When the 
armature attains full speed, the arm comes in contact 
with the little magnet M, and is held there by magnet- 
ism. The whole object of the starting box is to check 
the inrush of current, while the armature is developing 
its counter E. M. F. or back pressure. 

When the armature has attained its normal speed, 
the starting box is no longer in use. If for any reason 
the current ceases to flow, the little magnet M loses its 
magnetism and releases the arm, which (actuated by a 
spring) flies back and opens the circuit so that, should 
the current suddenly come on again, the sudden inrush 
will not damage the armature. 

In Fig. 64 are shown the connections of a series 
wound motor with an automatic release spool on the 
starting box of a sufficiently high resistance so it can be 
connected directly across the circuit. This becomes 
necessary since the field windings are in series with the 
armature. 

The speed of a series motor may be decreased by 
connecting a resistance in series with the motor and 
may be increased in speed by cutting out some of the 
field windings. In electric railway work where two 
motors are used on one car, they are usually connected 
in series with each other in starting up and then in 
parallel with each other while running at full or nearly 
full speed. The series motor is well adapted to such. 



112 



ELECTRICITY FOR ENGINEERS 



work as electric railway work, or for cranes and so 
forth, because it will automatically regulate its speed 
to the load to be moved, exerting a powerful torque 
at a low speed while pulling a heavy load. Such a 
motor, however, requires constant attendance when the 




FIGURE 64. 

load becomes light, as it will tend to "run away" 
unless its speed is checked. 

In Fig. 65 we have a diagram of a compound wound 
motor connected with a type of starting box that cuts 
out the armature when current has been cut off the 
lines supplying the motor, as before explained. In 
addition to this there is another electro magnet which 
is traversed by the main current on its path to the 
armature. Should the motor be overloaded by some 



ELECTRICITY FOR ENGINEERS 



113 



means, the current flowing to the armature would 
exceed the normal flow. The magnetism thus pro- 
duced would overcome the tension of a spring on the 
armature of the so-called "overload magnet" and cause 
it to short circuit the magnet which holds the resist- 
ance lever and allow it to fly back and open the arma- 




FIGURE 65. 

ture circuit. By so doing the liability of burning out 
the armature due to overload is reduced to a minimum. 
The compound motor may be made to run at a very 
constant speed, if the current in the series winding of 
the fields is arranged to act in opposition to that of the 
shunt winding. In such a case an increase in the load 
of a motor will weaken the fields and allow more cur- 
rent to flow through the armature without decreasing 



114 



ELECTRICITY FOR ENGINEERS 



the speed of the armature, as would be necessary 
in a shunt motor. Such motors, however, are not 
very often used, since an overload would weaken the 
fields too much and cause trouble. 

If the current in the series field acts in the same 




FIGURE 66. 

direction as that of the shunt fields, the motor will 
slow up some when a heavy load comes on, but will 
take care of the load without much trouble. Fig. 66 
shows a starting box arranged as a speed controller. 
It differs from other starting boxes only in so far that 
the resistance wire is much larger and that the little 



ELECTRICITY FOR ENGINEERS 115 

magnet will hold the arm at any place we desire, so 
that if we leave the arm at any intermediate point the 
motor will run at reduced speed. This sort of speed 
regulation can be used only where the load on the 
motor is quite constant. If the load varies, the speed 
will vary. Another and a better way of varying the 
speed of motors consists in cutting a variable resist- 
ance into the field circuit, as more resistance is cut 
into the circuit the fields become weaker and the 
motor speeds up. If possible, motors should be so 
designed that they can operate at their normal speed, 
and they will then cause little trouble. 

Motors have much the same faults as dynamos, but 
they make themselves manifest in a different way. 
An open field circuit will prevent the motor from start- 
ing and will cause the melting of fuses or burning out 
of an armature. The direction of rotation can be 
altered by reversing the current through either the 
armature or the fields. If the current is reversed 
through both, the motor will continue to run in the 
same direction. A short circuit in the fields, if it cuts 
out only a part of the wiring, will cause the motor to 
run faster and very likely spark badly. If the brushes 
are not set exactly opposite each other, there will also 
be bad sparking. If they are not at the neutral point, 
the motor will spark badly; brushes should always be 
set at the point of least sparking. If it becomes neces- 
sary to open the field circuit, it should be done slowly, 
letting the arc gradually die out; a quick break of a 
circuit in connection with any dynamo or motor is not 
advisable, as it is very likely to break down the insula- 
tion of the machine. 

The ordinary starting box for motors is wound with 
comparatively fine wire and will get very hot if left in 



116 ELECTRICITY FOR ENGINEERS 

circuit long. The movement of the arm from the first 
to the last point should not occupy more than thirty 
seconds, and if the armature does not begin to move at 
the first point the arm should be thrown back and the 
trouble located. 

Alternating Current Motors. By a proper combination 
of two phase or three phase currents it is possible to 
produce a revolving magnetic pole. By placing inside 
of the apparatus which produces this revolving mag- 
netic pole a suitable short circuited armature, this 
armature will be dragged around by the revolving pole 
in much the. same way that a short circuited armature 
in a direct current machine would be dragged around 
if the fields were revolved. Such a machine is called 
an induction motor. The armature will revolve with- 
out any current entering it from the external circuit. 
This does away with commutators, collector rings, 
brushes, brush-holders, and in fact many of the parts 
which are so necessary in direct current machines. 
The rapidity of the alternations in the external circuit 
determines the speed of the motor. 

Some alternating current motors are known as 
"synchronous" motors. What is meant by synchro- 
nous is, occuring at the same time, or in unison. As 
an example, suppose two clocks are ticking just alike 
so that the pendulums start and stop at the same time; 
we would hear but one tick. These two clocks would 
then be in synchronism. If an alternating current 
generator has 32 field coils and revolves at the rate of 
60 R. P. M., then a synchronous motor with only 4 
field coils would revolve at the rate of 480 R. P. M. 
This motor would operate in synchrony with the gener- 
ator and yet would make 480 R. P. M. while the 
generator made 60 R. P. M. 



CHAPTER VI 

Fuses and Circuit Breakers. Fuses are metal wires or 
strips, generally made of an alloy of lead and antimony, 
the amount of each metal used being so proportioned 
that the wire will melt at a certain temperature. This 
metal is very similar to that used in the fusible plugs 
in boilers. These fuse strips or fuse wires are placed 
in the various circuits in such a manner that the current 
must first flow through the fuse before entering the lights, 
motors or other electrical apparatus. If a short circuit 
should occur, there would be an excessive amount 
of current flow through the fuse and the temperature 
of the metal would be raised to the point where it would 
melt and open the circuit. This would cut off the current 
and save the electrical apparatus from being damaged 
by the excessive current. Fuses are placed in the var- 
ious circuits in accordance with the rules and regulations 
of the National Board of Fire Underwriters. These rules 
require a fuse to be placed in the circuit of every piece 
of electrical apparatus liable to be short circuited, and 
also at points where small wires are tapped onto larger 
ones, unless the main fuse in the larger wire is small 
enough to protect the smallest wire in the circuit. The 
ordinary commercial fuse wire is not intended to melt 
until the current has reached a strength of about twice 
the number of amperes marked on the fuse. A few 
good points to remember in regard to fuses are as fol- 
lows: Unless the fuses are of the new enclosed type 
(fuses entirely encased in small tubes) or unless they 
are under the eye of a constant attendant, they should 
be enclosed in fireproof boxes. This should be done 
to minimize the chance of the red hot metal from a 
117 



118 ELECTRICITY FOR ENGINEERS 

melted fuse dropping into some inflammable material. 
It is a very good plan to enclose all fuses. Fuses 
placed in a hot room will blow at a lower increase in 
current than those in a cool room. Always use copper 
tipped fuses, both for the purpose of getting a good 
contact at the binding screw and for the reason that 
the blowing point of a fuse wire depends on the length 
of the wire. Two pieces of fuse wire of the same 
diameter, but of different lengths, will not blow with the 
same current because the cooling effect of the terminals 
is greater with the shorter fuse. 

In the larger size fuse strips see that the contacts 
between the fuse terminal and the binding post are free 
from dirt and that there is plenty of contact between 
them, otherwise the poor contact will heat up the ter- 
minal and the fuse strip and cause it to blow at a much 
lower current strength than that for which it is marked. 
Oil between the contacts will cause heating and the 
same result. 

From the fact that when a fuse strip has blown the 
current will be off the circuits which are protected by 
the strip until the fuse has been replaced, and this 
takes some time, another device known as the circuit 
breaker has come into general use. The circuit breaker 
is simply a knife switch equipped with a spring which 
tends to open it, and is held in place by a small catch. 
The current passing through the switch also passes 
through the winding of a small solenoid on the inside 
of which is an iron core. When the current passing 
through the solenoid exceeds a certain amount, the 
iron core is drawn up into the solenoid, and in doing 
so strikes the catch holding the switch and releases it, 
thus opening the switch and cutting off the current. 
Circuit breakers are nearly always installed in the cir- 



ELECTRICITY FOR ENGINEERS 



119 




FIGURE 67. 



120 ELECTRICITY FOR ENGINEERS 

cuits of generators, although fuses are also used. The 
fuse is rated higher than the circuit breakei, so that 
the circuit breaker will operate first and the fuse only 
operates when the circuit breaker fails to work. Cir- 
cuit breakers are also used to a large extent in protect- 
ing large motors, and the small overload devices used 
on motor starting boxes are simply circuit breakers. 
Fig. 67 shows a view of an I-T-E circuit breaker. S is 
the solenoid and I the moveable iron core. This core 
is adjustable, by means of the washer W, so that it will 
operate at whatever current desired. L is the catch 
which holds the switch. Carbon contact pieces, C C, 
are so arranged that the current is broken on them, 
thus taking the arc off the blades. In Fig. 68 a dia- 
gram of a circuit breaker used for the protection of a 
motor is shown. In this case the circuit breaker is 
double pole; while the one shown in the preceding fig- 
ure is single pole. 

For small work, such as tap lines and small motors, 
the circuit breaker is too expensive to warrant its use, 
but for capacities of 50 amperes and over it is advisible 
to use the circuit breaker. . Circuit breakers are also 
designed and used to prevent the liability of short cir- 
cuits between generators connected in parallel, due to 
the reversal of polarity of one of the dynamos. In other 
words, should one of the dynamos become reversed in 
polarity while working in parallel with other machines, 
the polarity circuit breaker would open the machine- 
switch and cut it out. Circuit breakers of this descrip- 
tion are also used in charging storage batteries. Some- 
times circuit breakers are referred to as overload 
switches. The mechanical operation of these instru- 
ments can be readily understood when examined, as 
they are all of a very simple mechanical construction. 



ELECTRICITY FOR ENGINEERS 12 J. 

LINE 




;r CIR CUIT 
BREAKER 



D.P.S.T. 
SWITCH 



FIGURE 68 



CHAPTER VTI 

ALTERNATING CURRENT DYNAMOS 

Alternating current dynamos^are operated upon the 
same general principle of magnetic induction as that 
involved in continuous current dynamos. The 
mechanical construction, however, differs considerably 
in the two types of machines. The current produced 
in the two types is identical, but in the direct current 
machine this current is rectified by means of a com- 
mutator; that is, the current constantly flows out or; ; 
wire and back in the other wire, never changing in 
direction in the external circuit. In the alternating 
current dynamo the current is sent to the line exactly 
as it is generated in the armature, flowing out one wire 
and back on the other and then reversing and flowing 
out on the wire on which it has just flowed in, and back 
on the wire on which it had formerly flowed out. An 
illustration which will more fully explain this action 
can be found by supposing the two ends of the cylinder 
of a piston pump were connected by means of a pipe 
and then, having done away with all the valve move- 
ments, the pumps were started. At the beginning of 
the stroke, water would be forced out one side of the 
cylinder around the pipe into the other side of the 
cylinder, and after the piston had reached the end of 
the stroke and started back, the water would then take 
a return course back to where it had started. In this 
case the pump could be likened to the dynamo and 
the pipe to the wires, and the current to the water 
flowing back and forth. The form and winding of 
122 



s 



ELECTRICITY TOR ENGINEERS 



123 



alternating current dynamos varies considerably, but 
they generally follow the plan shown in Fig. 69. In 
the figure the pole pieces are alternately north (N) and 
south (S), while the armature is wound with the same 
number of poles, with the winding so arranged that 
the poles alternate. The fields are excited by direct 
current passing over the field coil windings. This 




figure 69. 



direct current is usually obtained from another source 
aside from the current generated in the armature of 
the alternating current dynamo. A separate dynamo, 
called an exciter, is employed for supplying the cur- 
rent to the fields. There are some types of so called 
"composite wound alternating current dynamos" in 
which a part of the current from the alternator arma- 



124 



ELECTRICITY FOR ENGINEERS 



ture is rectified or commutated by means of a commu- 
tator mounted on the same shaft with the armature, 



Armatures are wound 
in two layers. 

.__ upper coil. 

lower » 



FIGURE 70. 




and this commutated current passed around the field 
coils in a manner similar to the direct current com- 



ELECTRICITY FOR ENGINEERS 125 

pound wound dynamo. In Fig. 70 we have a diagram 
of connections of a composite wound machine made by 
the General Electric Company. It will be noticed that 
in connection with this dynamo we still employ a sepa- 
rate direct current exciting machine. The object of this 
composite winding is the same as with the compound 
wound direct current dynamo, namely, regulation 
under variable loads without the necessity of changing 
the strength of the field exciting current from the 
exciter dynamo. The winding of the alternate current 
armature consists of the same number of armature coils 
as there are pole pieces in the fields of the machine. 
The outer end of the first armature coil is left free to 
be connected to one of the collector rings, while the 
other end of the coil is connected to the inner end of 
the second coil; the outer end of the second coil is 
connected to the outer end of the third coil, and so on 
through the entire armature. In this class of winding 
you can readily see that while the coils connected from 
the underside or inner ends are under the influence of 
one polarity of field magnetism, the armature coils 
connected from the outer side are under an opposite 
magnetic influence. The purpose of forming the arma- 
ture circuit m this manner may be fully understood 
when it is remembered that the magnetism from the 
north pole of a magnet will induce a flow of electricity 
in a coil of wire in a given direction, while the mag- 
netism of the south pole will induce a flow of current 
in an opposite direction. Now, for the reasons just 
explained, the current in all of the coils of the arma- 
ture will flow in the one direction, but as the armature 
is rotated sufficiently to move the coils from the influ- 
ence of one pole to the influence of the opposite pole 
which is next to it, the action of all the magnetic poles 



126 ELECTRICITY FOR ENGINEERS 

of the field reverse all the inductions in the armature 
coils and cause the current to flow in an opposite 
direction. The number of reversals occurring during 
a revolution is determined by the number of poles that 
the armature coils pass during one revolution. One of 
these armature coils we will assume to be under a 
north magnetic influence and in its rotation it passes 
through a south magnetic influence, thence into a 
north magnetic influence again. The current has now 
alternated or reversed its direction of flow twice and 
has passed through what is called one cycle. If the 
current were making 120 alternations or passing 
through 60 cycles in one second, it would be known as 
making 60 cycles or alternating at the rate 7,200 alter- 
nations per minute. These are the general terms used 
in designating alternating currents. 

By tracing out the circuits' in Fig. 70, it will be seen 
tnat, assuming the current to be flowing into the col- 
lector ring R, it will pass through the upper half of the 
armature winding and out to the commutator C, where 
a part of it will be commutated (or changed into direct 
current), then flowing back around the lower half of 
the armature windings and out to the other collector 
ring R\ On the commutator C the upper line coming 
from the armature is connected to each alternate seg- 
ment, while the lower line is connected to the remain- 
ing segments. The amount of current which is thus 
rectified and flows around the two halves of the field 
winding, which are connected in parallel, is regulated 
by means of the German silver shunt. The fields are 
also energized by the current generated in the small 
dynamo known as the exciter. 

In Fig. 71 is shown an alternating current dynamo 
with its separate exciter The two collector rings are 



ELECTRICITY FOR ENGINEERS 



127 



shown immediately at the right of the armature, while 
at the right of the collector rings is shown the commu- 
tator from which the current for the composite winding 
of the fields is taken. The current generated by the 
alternator is regulated in the same way as with direct 
current dynamos; that is, by varying the current sent 
around the field windings. This is accomplished by 
the use of a resistance box in series with the exciting 




FIGURE 71. 



current or by means of a resistance box connected in 
the fields of the exciting dynamo. This latter regula- 
tion is of course the more economical, as there would 
be considerable energy wasted were a resistance used 
in the main exciting circuit. Alternating currents are 
generally used where currents are to be transmitted 
long distances, as for instance, where power is derived 
from a water fall situated some distance from the 



128 



ELECTRICITY FOR ENGINEERS 



point of use Its adaptability for such work is 
apparent, because it can be generated at high voltages 
and transformed down to any voltage desired. It 
requires less copper to transmit it, due to the higher 
voltages employed. By the aid of transformers it can 
either be stepped up to a higher pressure or stepped 
down to as low a pressure or voltage as .desired. 
Another great advantage is that, after it has been 
transmitted a considerable number of miles, by the aid 




figure 72. 



of a rotary converter it can be converted into direct 
current. 

Rotary transformers which transform the alternating 
current to a direct current are simply alternating cur- 
rent motors connected to direct current dynamos. 
Sometimes these machines are mounted on the same 
shaft; sometimes they are belted together, and in some 
cases the same windings are used for both machines; a 
commutator being mounted at one side of the armature 



ELECTRICITY FOR ENGINEERS 129 

from which direct current is taken while the alter- 
nating current is taken into the armature on a pair of 
collector rings on the opposite end of the shaft. In 
Fig. 72 is shown a view of a rotary transformer where 
the alternating current is taken in at the right, and 
direct current taken off at the commutator on the left. 
By single phase we understand that the current flows 
out, gradually increasing in strength, then dying away 
and reversing in direction and again increasing and 
dying away. This action is shown by the curve in 




figure 73. 

Fig. 73. Although the single phase alternating cur- 
rent system is in advance of the direct current system 
for electrical power transmission, because permitting 
electrical power to be transmitted long distances at 
high potential, which can be readily increased or 
reduced by means of transformers, the single phase 
system is limited by the difficulty in obtaining a satis- 
factory self starting motor; therefore the use of the 
single phase current has been confined almost entirely 
to transmitting current for lighting. The development 
of the polyphase (two phase_ and three phase) alter- 



130 



ELECTRICITY FOR ENGINEERS 



nating systems possess all the advantages of the single 
phase system and at the same time permits the use of 
motors having not only most of the valuable features 
of the continuous current motors, but also some advan- 





figure 74. 



tages over them. In the two phase system two cur- 
rents displaced 90 degrees from each other and 
otherwise exactly similar to the single phase currents 
are used. In the three phase system three currents 
separated 120 degrees are used. These currents are 
shown in Fig. 74. 




FIGURE 75. 



In Fig. 75 is shown the principle upon which the 
transformer used in alternating current work are opera- 
ted. Two separate coils of wire are wound on a ring 



ELECTRICITY FOR ENGINEERS 



LSI 



of laminated iron. One of the coils contains a num- 
ber of turns of fine wire, while the other contains only 
a few turns of large wire. When an alternating cur- 
rent is sent around the coils of fine wire, generally 
called the primary, a current will be induced in the 
coil of heavy wire, or secondary. The amount of cur- 
rent induced in the larger wire will be relatively 
greater in amperes and less in potential than that of 
the fine wire circuit. This ratio is almost entirely 
dependent upon the relative number of turns existing 




FIGURE 76. 



between the large and the small wires. To illustrate, 
suppose we had a current of 10 amperes at a pressure 
of 1,000 volts in the primary, and there were ten times 
as many turns of wire in the primary coil as in the 
secondary, then we would get a current of ioo amperes 
at a pressure of ioo volts in the secondary coil. This 
same relation would hold true whatever the ratio 
between the number of turns on the two coils might 
be. In Fig. 76 is shown a core of iron having on one 
end a primary coil connected to a battery. On the 
other end of the core is another coil connected to the 



132 ELECTRICITY FOR ENGINEERS 

ends of which is an incandescent lamp. By making 
and breaking the battery circuit the lamp may be made 
to flash up, due to the great voltage induced in the 
secondary coil. This is a good thing to remember 
when working with a dynamo or motor. Do not 
quickly break the shunt field connection, as the 
increased voltage due to the current induced by the 
field magnet when the circuit is broken is liable to 
puncture the insulation and necessitate the re-winding 
of the field coil. 



CHAPTER VIII 
METERS 

Volt and Ampere Meters. Two of the most important 
instruments used in electrical work are the voltmeter 
and amperemeter, the latter generally called ammeter. 
Classed with these instruments, is a meter of an im- 
portant nature called the wattmeter. We will first 
become acquainted with the voltmeter, which is an 
instrument, as its name implies, for measuring the 
voltage or potential or electromotive force between two 
wires. The general construction of this instrument .is 
shown in Fig. JJ. 

In this diagram we show an instrument on the order 
of the Weston meter. This will serve as a good illus- 
tration that the operation of meters is very similar to 
the operation of motors. A permanent magnet, M, 
causes a magnetic flux across the air gap G, and 
situated in this gap is a bobbin, B, on which is wound a 
number of convolutions or turns of copper wire. The 
bobbin is made to revolve on jeweled bearings. The 
object of the jewel bearing is to have the instrument as 
much devoid of mechanical friction as possible. Two 
springs, S, one above and one below the bobbin, carry 
the current to the movable part of the meter. If the 
current is now caused to flow around the coil of wire, 
it will produce a torque or twist which will move the 
bobbin again the two hair springs, S. Like magnetic 
poles repel each other and unlike magnetic poles 
attract each other. The current flowing around the 
133 



134 



ELECTRICITY FOR ENGINEERS 



movable bobbin produces magnetism, and the quantity 
or strength of magnetism so produced is proportional 
to the amount of current which the pressure or voltage 




figure 77. 



will force through the winding of the movable bobbin 
so that the bobbin will continue to move until the 
torque exerted by the current equals the counter torque 
exerted by the spiral springs. A pointer, fastened to 



ELECTRICITY FOR ENGINEERS 135 

the shaft upon which the bobbin is mounted, passes 
over a graduated scale and indicates the pressure or 
volts. The capacity of this meter in volts will vary as 
the resistance of the wire connected in series with the 
bobbin varies. We will assume that we have a meter 
whose pointer reads from o to 125 volts. If we desired 
this same meter to read from o to 250 volts, we would 
put a resistance in the meter which would be twice as 
great as the one contained in the meter when reading 
from o to 125 volts. The permanent magnet of this 
meter is made of Tungsten steel, and this steel is arti- 
ficially aged so that when the instrument leaves the 
factory the magnetizing power of the magnet will 
remain constant for a number of years. The current 
is brought into the instrument through the binding 
posts A and C, but before passing through the wire on 
the bobbin the current must pass over a path of very 
high resistance, R. This resistance is proportioned to 
the amount of pressure the meter is made to indicate, 
and in commercial construction instead of making 
bobbins of variable resistances, the bobbins are all 
made alike, and this dead resistance, R, is varied to 
comply with the pressure that it is to indicate with the 
instrument. In voltmeters used on a 500 to 600 volt 
circuit, this resistance will measure from 65,000 to 
75,000 ohms. The current which flows through the 
winding on the bobbin at full voltage is very small, and 
when registering no volts amounts to about one seven- 
hundredth of an ampere. Since it is the number of 
ampere turns that produces the magnetic density in an 
electro magnet, it can be seen that even one seven- 
hundredth of an ampere, if passed around a bobbin a 
considerable number of times, will produce quite a 
strong magnetic flux and pull. Voltmeters are often 



136 ELECTRICITY FOR ENGINEERS 

referred to as being "dead beat." What is meant by 
dead beat is the tendency of the pointer to move from 
one position to another with very little or no swinging 
to and fro. In this type of voltmeter this dead beat 
effect is producedin the following manner: The core 
of the bobbin B being constructed of copper, when a 
current flows over the winding of the bobbin and causes 
it to revolve, eddy currents are produced in the copper 
(in much the same way that current is produced in the 
revolving armature of a dynamo), and these eddy cur- 
rents tend to arrest the motion of the bobbin. In the 
best voltmeter construction the resistance wire used is 
made of a metal which will not vary much in resistance 
at different temperatures. It can readily be seen that, 
were a meter which was constructed and correctly 
calibrated at 70 ° F., surrounding temperature, mounted 
on switchboard in an engine-room with the temperature 
at 90 or 95°, the meter would uot register absolutely 
correct, because the resistance of the wire would be 
considerably increased, due to the increase of the sur- 
rounding temperature. The effect of this would be a 
smaller flow of current at an equal voltage through 
the bobbin in the meter, and consequently a smaller 
amount of magnetism and a lower reading of the in- 
strument. 

We will assume that a copper cable of about the size 
of one's wrist is conducting a current of about 
three thousand amperes. Now, if a monkey wrench or 
hammer were to be lying within a few inches of this 
cable, before current was flowing, the monkey wrench 
or hammer would be attracted to the cable. The 
rapidity with which the monkey wrench would be 
attracted to the cable would be proportional to the 
weight of the iron in the wrench and the amount of the 



ELECTRICITY FOR ENGINEERS 137 

current flowing through the cable. This, I think, will 
explain an electrical phenomenon which will assist us 
to understand what are called the magnetic vane volt- 
meters and ammeters. This principle is shown in 
Fig. 7 S. 

A certain amount of current passing over the path 
A, which consists of several turns of wire, will attract 
an iron form, B, mounted on the spindle with the 




FIGURE 78. 

pointer. The attraction will be proportional to the 
amount of current flowing over the copper conductor. 
The advantage of such an instrument is its simplicity, 
but the disadvantage is its inaccuracy. Its simplicity is 
apparent, and its inaccuracy is due to the residual 
magnetism that remains in the iron part B when the 
current through the conductor has been reduced. 
When the indicator is caused 1o move upward on the 
scale, the instrument will register practically correct, 



138 ELECTRICITY FOR ENGINEERS 

but as the flow of current over the conductor A dimin- 
ishes or decreases, the residual magnetism remaining 
in the iron part B will have a tendency to cause it to 
lag back. Amperemeters are constructed on practi- 
cally the same lines as explained in the construction of 
voltmeters, except that in ammeters the whole current 
to be measured passes through the coil A, this coil 
being made of comparatively few turns of large wire, 
while in voltmeters the resistance is very high. 
Ammeters are placed in series with one of the leads 
and voltmeters in shunt with the current to be meas- 
ured. In some ammeters a resistance block, usually 
called a shunt, is employed, over which the main cur- 
rent is caused to flow, and the ammeter is connected to 
both ends of this resistance block. In this way only a 
very small portion of the total current is caused to 
flow through the ammeter. In this case a milli-volt- 
meter, with the scale graduated to amperes, is 
employed. By Ohm's law we know that the voltage is 
equal to the current times the resistance, E = CR. 
The resistance remaining constant, the voltage is pro- 
portional to the current, so that the amount of current 
sent through the milli-voltmeter or ammeter is exactly 
proportional to the current flowing through the shunt. 
Fig. 79 shows connections for ammeters which carry 
the entire current and those used with a shunt. 

The object of such a construction is apparent. In 
the installation of the switchboard, where each 
ammeter registers several thousand amperes, it is not 
necessary to construct the large conductors in such a 
manner that the total current is caused to flow through 
the ammeter. For each 1,000 amperes passing over 
the shunt only about one-half an ampere will pass 
through the ammeter, and the little bobbin will then 



ELECTRICITY FOR ENGINEERS 



139 



cause a deflection of the pointer in the meter and the 
pointer will register 1,000 amperes. Meters of this 
description are usually connected to their resistance 
blocks by a pair of No. 16 flexible lamp cords. When 
installing meters of this class, never cut off any of the 




/~\ 




</ 



gHUHt 



t<* 



FIGURE 79. 



flexible cord which is supplied with the ammeter, as 
the resistance of the cord becomes a part of the resist- 
ance in the meter. By cutting off some of this cord 
it can be readily seen that the meter will register more 
current than it should. 



140 



ELECTRICITY FOR ENGINEERS 



Another kind of meter is constructed on the 
solenoid principle, and is shown in Fig. 80. In this 
instrument the helix is a bare copper wire and is wound 
in an open coil form. It is curved in the shape of a 
segment of a circle, the center of which is at the pivot 
on which the needle is suspended. The pointer or 
needle is attached and projects downward to the scale. 
The helix is made of copper rod or is cast to the shape 





./^ * ^^"^ m 




\ \ / 1\ \ 
\ » / / 1 1 

V * / / J I 

\ V / / J 



FIGURE 80. 



required. Being of an open coil type, it is not neces- 
sary that it be insulated with insulating material 
because the air spaces between the turns becomes the 
insulation. Although not the best insulator by any 
means, there are few substances which possess better 
insulating qualities than air, although on account of its 
absorption of moisture, it becomes often a much poorer 
insulator than many other materials. In this type of 



ELECTRICITY FOR ENGINEERS 



141 



instrument it will be seen that as the number of 
amperes flowing over the coil is increased it produces 
an increased electromagnetic pull on the iron section 
or core entering it. As this electro magnetic pull is 




FIGURE 81. 



increased, the core moves up into the helix and causes 
a deflection of the pointer across the scale on the 
instrument. This type of instrument has the same 
objection as that of the magnetic vane instrument, 



142 ELECTRICITY FOR ENGINEERS 

namely, residual magnetism of the iron, and hence 
error in the reading while the current flowing is being 
diminished. 

Another style of simple ammeter or voltmeter is 
shown in Fig. 81. This instrument consists of a frame 
made of non-magnetic material, around which the wire 
is wound, the ends of the wires being connected to the 
binding posts. The armature of this instrument, as in 
all other similar instruments, is connected to the 
pointer, and may be constructed of several pieces of 
iron. The principle of its working is similar to that 
described above, in that the armature tends to set 
itself at right angles, to the wire through which the 
current passes. This style of instrument is used where 
current is liable to flow in either direction. 

A simple form of meter for measuring current is 
shown in Fig. 82. Here we have an amperemeter 
which consists of a strip of copper fastened to a block 
of wood or other insulating material, as shown at A. 
A piece of magnetized steel, B, to which a needle, C, is 
attached, swings on a pivot or shaft which is suspended 
at the bridge D. A scale is provided from which the 
number of amperes flowing can be obtained. The 
needle is rigidly attached to the magnetized steel B and 
moves with it. The action of this instrument is as fob 
lows: When a magnetized piece of steel is brought near 
to a conductor through which a current of electricity 
is passing, the magnetized steel tends to set itself at 
right angles to the direction of the current. The 
stronger the current becomes, or the more highly mag- 
netized the piece of steel may be, the nearer to a posi- 
tion of right angles the armature will assume. It is 
not practical to use this construction of an instrument 
to cover a range of more than one-half of a right 



ELECTRICITY FOR ENGINEERS 



143 



angle, for when the needle moves through an angle of 
about 50 degrees, it will require a much greater 
increase of current in proportion to the movement to 
obtain the deflection and the additional degree of the 
indicating needle. Such an instrument as the above 
may also be used to determine the direction of flow of 




FIGURE 82. 



current in a wire and is sometimes quite- convenient on 
arc circuits which are liable to have their currents 
reversed either by wrong plugging of the board or the 
reversing of polarity in the dynamo. 

Voltmeters and ammeters used with alternating cur- 
rents must, of course, differ in some respects from 



144 ELECTRICITY FOR ENGINEERS 

those employed for continuous currents. Alternation 
of the current does not permit the utilizing of the mag- 
netic effect of the current to the same extent or in 
exactly the same manner as continuous currents, but 
when the cores of magnets are built up of soft iron 
wires of small diameter, the resulting attraction 
between coil and core is similar, though not so strong 
as between a coil carrying direct current on a solid 
iron core. 

Another type of ammeter and voltmeter used with 
alternating or direct current is known as the hot wire 
instrument. A rather long, thin platinum wire is 
placed in the circuit and so arranged that its elonga- 
tion or expansion resulting from the heating effect of 
the current passing over it is made to operate a pointer 
mounted on a jeweled bearing. These instruments 
absorb but little current and are claimed to be per- 
manently correct. This class of instrument may be 
used on either direct or alternating current, and when 
used on alternating current the frequency or alterna- 
tions make no difference in the operation of the instru- 
ment. It is also unaffected by external magnetic fields, 
such as a neighboring dynamo or motor, and can be 
used close to a wire conducting current without being 
affected in its accuracy. When used as an ammeter it 
is connected in shunt with a resistance placed in the 
main circuit in the same manner as described for direct 
current ammeters, and in this way but a very small 
proportion of current is made to pass over the instru- 
ment. Separate resistances are also furnished with the 
instruments; so that by connecting these in series with 
the instrument they can be used over a very wide range. 

Wattmeters. A few years ago, where current was 
sold by central stations to consumers, or in any other 



ELECTRICITY FOR ENGINEERS 145 

place where it was desirable to measure the power fur- 
nished in the form of electricity, there were several 
kinds of differently constructed meters used to measure 
the amount of current. Some of these meters were 
based on the chemical action of the current; the current 
in passing to the work depositing metal from one plate 
to another. The plates or terminals of the meters 
were weighed before being placed in the circuit and 
again weighed on being taken out, the amount of metal 
having been deposited determining the amount of cur- 
rent used, as explained in the fore part of the book. 
Of late, however, most of the recording wattmeters in 
use are operated on the principle of the Thomson 
wattmeter. As has been explained under the definition 
of units, the work done (watts) is equal to the current, 
(amperes) multiplied by the electromotive force (volts), 
or W = C x E. For a wattmeter to register correctly it 
must take a record of the volts and amperes. 

The Thomson wattmeter is simply a small motor in 
which the armature is used as a voltmeter and the 
fields as an ammeter. The armature is wound with fine 
wire and is connected to a small commutator made up 
of metal bars. Two very thin metal brushes bear on 
this commutator and carry the current to and from the 
armature. The armature is connected across the mains 
in just the same wav as a voltmeter would be connected. 
The fields are wound with a coarse wire and are con- 
nected in series with the main circuit, thus acting as an 
ammeter. It can readily be seen that with the arma- 
ture influenced only by the voltage, and the fields by 
the current passing through the mains, the two acting 
together will correctly measure the power supplied. 
As the voltage rises or lowers, the speed of the arma- 
ture will be affected accordingly, and as the current 



146 



ELECTRICITY FOR ENGINEERS 



through the fields varies the electromagnetic effect 
produced by the fields and in which the armature 
revolves will vary, thus also varying the speed. By 
reference to Fig. 83, the fields F F are connected in 
series with one of the mains and the armature A is. 




FIGURE 83. 



connected across the mains. Fig. 84 is a simplified 
diagram. Attached to the shaft on which the arma- 
ture rotates is a copper disc which revolves between 
the poles of a permanently magnetized steel magnet. 
Eddy currents are generated in this copper disc as the 



ELECTRICITY FOR ENGINEERS 147 

armature rotates, thereby acting as a brake against 
which the armature must work. Connected to the top 
of the shaft is a train work of wheels which move small 
pointers over the dials on the face of the instrument 
and record the amount of current which has passed 
through the meter. As no iron is used in either the 
armature or fields of the motor, the meter can be used 
on either alternating or direct current. 

In Fig. 85 we show a two wire meter with the case 
removed. 

In Fix. 86 a three wire meter is shown. 

Directions for Reading Meter Dials. To correctly read 
the sum indicated on the dial of a recording meter, the 



MA/VSWVWV 




directions given herewith should be thoroughly under- 
stood and carefully followed. 

The figures (1,000, 10,000, etc.) under or over each 
dial refer to a complete revolution of the hand at that 
dial. 

Therefore, each division on the dial to the extreme 
right indicates not one, two, three, or four thousands 
of units, but one, two, three, or four hundreds of units. 

A complete revolution of the hand counts one thou- 
sand, and will have moved the hand on the second dial 
one division. Thus in reading Diagram No. 6, Fig, 
87 the first dial (that on the extreme right) indicates 
700, not 7,000. 



148 



ELECTRICITY FOR ENGINEERS 



A hand to be read as having completed a division, 
must be confirmed by the dial before it (to the right). 
It has not completed the division on which it may 
appear to rest, unless the hand before it has reached 




FROM GENERATOR 



FIGURE 85. 



or passed o, or, in other words completed a revolution. 
For this reason it will be found easier and quicker to 
read a dial from right to left, as shown by reading Dia- 
gram No. 2, Fig. Sy. 



ELECTRICITY FOR ENGINEERS 



149 



The first dial (the extreme right) indicates 900. The 
second hand apparently rests on o, but since the first 
rests only on 9 and has not completed its revolution, 




FIGURE 86. 



the second dial also indicates 9. This 9, placed before 
the 900 already obtained, gives 9,900. 

This is also true of dial 3. The second hand, at 9, 
has not quite completed its revolution, so the third has 
not completed its division, therefore another 9 is 



1/50 ELECTRICITY FOR ENGINEERS 

obtained, making 99,900. The same is true of dial 4, 
making 999,900. 

The last dial (the extreme left) appears to rest on 1, 
but since the fourth is only 9, the last has not com- 
pleted its division, and therefore reads o. The total 
reading is 999,900. 

The hands are sometimes slightly misplaced. In 
Diagram No. 8 the first diagram (the extreme right) 
reads o, which gives. 000. The hand of the second 
dial is misplaced. As the first registers o, the second 
should rest exactly on a division; therefore it should 
have reached 8, making 8,000. The third hand is 
apparently on 3, but since the second hand is at 8, the 
third cannot have completed a division and must, 
therefore, indicate 2. The two remaining dials are 
correct, and make a total of 9,928,000. 

In Diagram No. 9, the second dial hand is mis- 
placed, for since the first indicates 1, the second should 
have just passed a division. As it is nearest to 8 it 
must have just passed that figure. The remaining 
three dials are approximately correct. The total indi- 
cation is 9,918,100. 

In Diagram No. 10, the second and fourth dial 
hands are slightly behind their correct position, but 
not enough to mislead in reading. The total indica- 
tion is 9,928,300. 

By carefully following these directions little diffi- 
culty will be found in reading the dial, even when the 
hands become misplaced. . 

Note whether there is a constant marked on the 
dial. If there is, multiply the dial reading by the 
constant. With constant y 2 , multiply by l / 2 ; that is, 
divide by 2. 

The "constant" of a meter is the term applied when 



ELECTRICITY FOR ENGINEERS 



151 



<0 



No.l- 1.111/100 



o^ (6 



No.6 = 99.700 



^OtASON REC0« 0//V( 
WATT METER 

ioooooooqenERAL ELECTRIC CO. ,0 °° 

WWatt Hrs. Constant Watt Hrs.CJ 




WATT METER, 

--GENERAL ELECTRIC CO. "><"» ^ 

(Jwart Hrs Constant Watt Hrs.vJ 
No. 3- 1.000.100 




ioooooooqeneral ELECTRIC CO. 100 ° -. 
vJwatt Hrs. Constant Wan HrsW 

No.4 =9.999.400 



'O 



c 



(fS , \^SON RE CO^ c ^o'^ 
X^y WATT METER X^fV 

.oooooooQENERAL ELECTRIC CO. ">°° 

vJWatt Hrs. Constant Watt Hrs.CJ 



No. 5 =^909.100 



O 



'b 



WATT METER 

100000006ENERAL ELECTRIC CO. «><>° ^ 
VJWatt Hrs. Constant Watt Hrs.Vj 




\^sj/ WATT METER 



10 oooooo G ENERAL ELECTRIC CO 1000 ^ 

(J Watt Hrs. Constant Watt Hrs VJ 



No.7 = 9.912.100 



o 



Ov 



o 



WATT METER 

GENERAL ELECTRIC CO. 100 ° 

Hrs. Constant Watt Hh. 



Q 



No. 8 =9.928.000 




o 



WATT METER 

iooooooogenERALELECTRIC CO " 00 ~ 

\J Watt Hrs. Constant Watt Hrs \Jj 



No.9=9.918.100 



<0 



WATT METER 

.ooooowqenERAL ELECTRIC CO. ,00 ° ^ 

\Cj Watt Hrs. Constant Watt Hrs.CJ 




'6~ 



No.10 = 9. 928.300 



1000000 100000 



"31 



Vjj/ WATT METER XjjJ 



.oooooooqenERAL ELECTRIC CO. ,00 ° ~ 
.Uwatt Hrs. Constant Watt HrsJJ 



FIGURE 87. 



152 ELECTRICITY FOR ENGINEERS 

the meter is constructed to run at a lower speed than 
what would be necessary to measure the true number 
of watts which has passed through it. For instance, 
if the constant is 2 and the meter has registered 5,000 
watt-hours, then the meter having run only half as fast 
as it should, we multiply 5,000 by 2, which gives us 
10,000 watts as the actual amount that has passed 
through the meter. This scheme becomes necessary in 
order to register a large amount of current with a 
meter small in bulk or size. For convenience the 
maker often takes a 220 voltmeter which would read 
the number of watts direct on the dial at 220 volts and 
sells it for a 110 voltmeter by marking a constant on 
the dial of the meter. 



CHAPTER IX 

Arc Lamps. The principle on which the arc lamp oper- 
ates is shown in Fig. 89. Current is caused to flow 
from one carbon point to another through a space or gap 
between the carbons. The heat of the arc is sufficiently 
high to disintegrate the carbon and reduce it to a vapor, 
this vapor filling the space between the carbon points. 
The current passes over this space in a bow-shape path 
or arc, and it is from this fact that the lamp gets its 
name. The arc is constantly moving, and generally 
revolves around the carbon points. This can be easily 
seen by looking closely at a burning lamp through a 
smoked glass. After a lamp has been burning for 
some time on direct current the carbons assume the 
shape shown in Fig. 88, the upper or positive carbon 
assuming a cup shape, while the lower carbon gener- 
ally burns to a point. This cup shape formation on 
the upper or positive carbon acts as a reflector to 
throw the light downward. The positive carbon burns 
away about twice as fast as the negative carbon and 
lamps must be trimmed accordingly. Sometimes the 
current feeding arc lamps (on direct current systems) 
becomes reversed, either through the dynamo reversing 
its polarity or through wrong plugging of the switch- 
board. The lamps will now burn "upside down," or, 
in other words, the bottom carbon will be the positive 
one. In such a case, if let go, the carbon holders of 
the lamp will be burned and the lamp will burn for 
only half the time for which it was intended, owing to 
the fact that the lower or negative carbon is only one- 
half as long as the upper or positive carbon. Such 3 
153 



154 ELECTRICITY FOR ENGINEERS 

condition can be determined by either of the following 
ways: See if the light is being thrown downwards. 
See which carbon is burning away the faster. Raise 
the carbons and notice the formation of the carbon 
tips. When the carbons are separated it will be 
noticed that the tip of one carbon is considerably hot- 
ter than the other and is heated a longer distance from 
the point; this is the positive carbon. 




FIGURE 88. 

The action of the arc lamp used on direct current 
constant current systems is shown in Fig. 89. Current 
passes through wire T and over the coarsely wound 
solenoid M, thence down to the carbon, across the 
arc or crater, into the negative carbon and out again 
on the wire T'. The regulating action is as follows: 
A coil M', constructed of fine wire and of high resist- 
ance, is connected in shunt across the arc. The action 
of the current flowing through the solenoid M across 



ELECTRICITY FOR ENGINEERS 



155 



Q T 



to 



the crater or arc produces a magnetic pull on the 
solenoid core A and causes a separation of the car- 
bons. As these carbons burn away the resistance 
across the crater increases and a very small portion of 
the main current is caused to flow through the shunt 
coil M\ The magnetic pull of the shunt solenoid 
overcomes that of the series solenoid with the result 
that the solenoid core A is drawn into coil M' and the up- 
per carbon thus lowered, de- 
creasing the gap at the arc. In 
this way a constant regulation 
is going on, tending to keep 
the two carbons at a uniform 
distance apart. The upper car- 
bon rod is held by means of a 
clutch. When the carbons have 
burned away, so that the lower- 
ing of the solenoid does not 
lower them to the proper ex- 
tent, the clutch is released and 
the carbon drops, thus feeding 
the lamp. Some lamps are 
manufactured wherein the lower 

carbon is positive. This causes the light emitted from 
the crater to be projected upwards. The arc lamp 
frame is supplied with a shade on which the light cast 
from the arc is reflected downward. The advantage of 
this system is to obtain a better diffusion and distribu- 
tion of the light beneath the arc lamp. This lamp 
is not now generally used. 

Fig. 90 shows a diagram of connections for the 
improved Brush arc lamp. These lamps are used on 
constant current or series systems and their action is 
as follows; 




156 



ELECTRICITY FOR ENGINEERS 



The carbons should rest in contact when the lamp is 
cut out. When the switch is opened, part of the cut- 




figure 90. 



rent from the positive terminal hook P goes through 
the adjuster to the yoke and thence through the carbon 



ELECTRICITY FOR ENGINEERS 157 

rod and carbons to the negative terminal hook N. 
The remainder of the current goes to the cutout 
block, but. as the cutout block is closed at first, the 
current crosses over through the cutout bar to the 
starting resistance, and so to the negative side of 
the lamp. A part of it, however, is shunted at the 
cutout block through the coarse wire of the magnets 
and so to the upper carbon rod and carbons and- out. 
This shunted current energizes the magnet and so 
raises the armature which opens the cutout and at the 
same time establishes the arc by separating the car- 
bons. 

The fine wire winding is connected in the opposite 
direction from the coarse wire winding, and its attrac- 
tion is therefore opposite. When the arc increases in 
length, its resistance increases, and consequently the 
current in the fine wire is increased. The attraction of 
the coarse wire winding is therefore partly overcome 
and the armature begins to fall. As it falls, the arc is 
shortened and the current in the fine wire decreases. 
The mechanism feeds the carbons and regulates the 
arc so gradually that a perfect, steady arc is main- 
tained. 

The fine wire of the magnets is connected in series 
with the winding of a small auxiliary cutout magnet 
at the top of the mechanism. 

This magnet, which also has a supplementary coarse 
winding, does not raise its armature unless the voltage 
at the arc increases to 70 volts. The two windings 
connect at the inside terminal on the lower side of 
auxiliary cutout magnet, and the current from the fine 
wire of the main magnets passes through both wind- 
ings and then to the cutout block and so to the starting 
resistance and out. 



158 ELECTRICITY EOR ENGINEERS 

If the main current through the carbon is interrupted 
(as by breaking of the carbons) the whole current of 
the lamp passes through the fine wire circuit. Before 
this excessive current has time to overheat the fine 
wire circuit, it energizes the auxiliary cutout mag- 
net, and closes a circuit directly across the lamp 
through the coarse wire on the auxiliary cutout to 
the main cutout block, and thence to the negative 
terminal. 

The auxiliary cutout operates instantly, and prevents 
any danger to the magnets during the short period 
required for the main armature to drop and throw in 
the main cutout. When the main cutout operates, the 
armature of the auxiliary cutout falls, because there is 
not sufficient current in that circuit to energize the 
magnet. 

The voltage at which the auxiliary cutout magnet 
operates depends on the position of its armature, 
which is regulated by the screw securing the armature 
in position. It should not be adjusted to operate at 
less than yo volts. 

One of the three methods of suspension maybe used 
for Brush lamps. If chimney suspension, which is the 
most common, is adopted, the wire, cable or rope used 
:o suspend the lamp must be carefully insulated from 
the chimney. For this purpose a porcelain insulator 
should be inserted between the support and the lamp, 
as shown in Fig. 91. 

Hook suspension may be used to advantage in some 
places, but great care must be taken to insulate the 
supporting wires from any conductors, as the hooks 
form the terminals of the lamps. 

The most convenient arrangement for indoor use is 
to suspend the lamp from a hanger board. The porce- 



ELECTRICITY FOR ENGINEERS 



1.59 



iain base of the hanger board prevents short circuits 
or grounds. 

A protecting hood is not necessary for outdoor use, 
as the lamp chimney and its base are one casting and 
effectual^' exclude rain or 
snow water. 

The lamps run on circuits 
of 6.6 amperes for 1,200 and 
9.6 amperes fcr 2,000 nom- 
inal candlepower. In case 
it is necessary to run a lamp 
on a circuit differing from 
the standard, the lamp may 
be adjusted by moving the 
contact on the adjuster. 
About one ampere either 
above or below the normal 
may be compensated for by 
this means. 

Permanent adjustment for 
special circuits of variation 
greater than one ampere is 
made by filing the soft iron 
armature. The clutch should 
be so adjusted that the cen- 
ter of the armature is f|- in. 
above the plate when the trip 
on the first rod is touching 
the bushing, and \\ in. when 

the trip on the second rod is in a similar position. 
A small gauge is convenient for adjusting the clutch. 
The position of the trip of the clutch determines the 
feeding point of the lamp. 

After thoroughly repairing and cleaning the lamp, it 




FIGURE 91. 



160 ELECTRICITY FOR ENGINEERS 

should be run a short time before installing. Lamps 
should not be tested in an exposed place, as a strong 
draft of air will cause unpleasant hissing which may be 
mistaken for some internal trouble. 

Lamps should not hiss or flame if good carbons are 
used. A voltmeter should always be used when adjust- 
ing or testing. 

The lamp terminals are marked P (positive) and N 
negative) and should be connected into circuit accord- 
ingly. 

The carbons should be solid and of uniform quality. 
For the best results, the upper carbon should be 
12 in. x T 7 g in., and the lower 7 in. x T 7 g in. The stub 
of the upper carbon may then be used in the lower 
holder when retrimming. 

At each trimming the rod should be carefully wiped 
with clean cotton waste. If any sticky or dirty spots 
; ppear, which cannot be readily removed with waste, 
^se a piece of well-worn crocus cloth, always being 
careful to use a piece of clean waste before pushing 
the rod into the lamp. It should never be pushed up 
'rto the lamp in a dirty condition. 

The carbon rod maybe unscrewed and removed by a 
small screw driver or small strip of metal inserted in 
the slot cut in the rod cap. The cap will remain in 
the hole through the yoke when the rod is taken 
out. 

In Fig. 92 an interior view of the Thomson-Houston 
arc lamp is shown. This lamp is also used on con- 
stant current systems. 

The lamps should be hung from the hanger boards 
provided with each lamp, or from suitable supports of 
wire or chain. 

As the hooks on the lamp form also its terminals, 



ELECTRICITY FOR ENGINEERS 



101 



they should be insulated, where a hanger board is not 
used, from the chains or wires used to support the 
lamp. 




figure 92. 



When the lamps are hung where the}/ are exposed to 
the weather, they should be covered with a metal 
hood, to prevent injury from rain and snow. 



162 ELECTRICITY FOR ENGINEERS 

In such cases, care should be taken that the circuit 
wires do not form a contact on the metal hood and 
short circuit the lamp. 

Before the lamps are hung up they should be care- 
fully examined to see that the joints are free to move, 
and that all connections are perfect. 

No lamp should be allowed to remain in circuit, 
with the covers removed and the mechanism exposed. 
Such practice is dangerous, and in violation of insur- 
ance rules. 

The object of testing the lamps in the station is to 
find any defects, if such exist, and to test all the con- 
ditions of running before delivering them to custom- 
ers. The lamps should not be hung up in their 
respective places in the external circuit, until every- 
thing is running with perfect satisfaction. 

The tension of the clamp which holds the rod is 
adjusted by raising or lowering the arm at the top of 
the guide rod. (See Fig. 93.) If the tension is too 
great the rod and clutch will wear badly and the feed- 
ing will be uneven, causing unsteadiness in the lights. 
Too little tension will not allow the clutch to hold up 
the rod and any sudden jar to the lamp will cause the 
rod to fall and the light to go out. 

The double carbon, or M lamp, should have the ten- 
sion of the second carbon a trifle lighter than the first 
one. 

When adjusting the tension, be sure to keep the 
guide rod perpendicular and in perfect line with the 
carbon rod; it should be free to move up and down 
without sticking. 

The tension of the clutch in the D lamp should be 
the same as that of the K lamp. It is adjusted by 
tightening or loosening the small coil spring from 



ELECTRICITY FOR ENGINEERS 



lt>3 



the arm of the clutch to the bottom of the clamp 
stop. 

To adjust the feeding point in the K lamp, press 
down the main armature as far as it will go, then push 




FIGURE 93. 



up the rod about one-half its length, let go the arma- 
ture and then press it down slowly and note the dis- 
tance of the bottom side of the armature above the 
base of the curved part of the pole. When the rod 



1()4 ELECTRICITY FOR ENGINEERS 

just feeds, this distance should be ]/^ in. If it is not, 
raise or lower the small stop which slides on the guide 
rod passing through the arm of the clutch, until the 
carbon rod will feed when the armature is ^ in. from 
the rocker frame at base of pole. 

To adjust the feeding point of the M lamp, adjust 
the first rod as in the K lamp. Then let the first rod 
down until the cap at the top rests on the transfer 
lever. The second rod should feed with the armature 
at a point T V in. higher than it was while feeding the 
first rod, that is, it should be T 5 g in. from rocker frame 
at base of pole. 

The feeding point of the D lamp is adjusted by slid- 
ing the clamp stop up or down, so that the rod will 
feed when the relative distances of the armature of the 
lifting magnet and the armature of the shunt magnet 
from rocker arm frame are in the ratio of I to 2. 
There should be a slight lateral play in the rocker, 
between the lugs of the rocker frame. 

The armatures of all the magnets should be central 
with cores, and come down squarely and evenly. 
There should be a separation of ^ m - between the sil- 
ver contact points, when the armature of the starting 
magnet is down. This contact should be perfect when 
the armature is up. The arm for adjusting the tension 
should not touch the wire or frame of the lamp when 
at the highest point. There should be a space of %\ in. 
or }i in. between the body of the clutch and the arm 
of the clutch, to allow for wear on the bearing surfaces. 

Always trim the lamp with carbons of proper length 
to cut out automatically, that is, have twice as much 
carbon projecting from the top as from the bottom 
holder. Always allow a space of }{ in., when the lamp 
is trimmed, from the round head screw in the rod, near 



ELECTRICITY FOR ENGINEERS 



165 



the carbon holder, to the edge of the upper bushing, so 
that there will be sufficient space to start the arc. 

The arcs of the 1,200 candlepower lamps should be 
adjusted to ¥ 3 ¥ in., with full length of carbon. Arcs of 
2,000 candlepower lamps should be adjusted from y 1 ^ 
to 3 8 *- in. when good carbons are used. 

The action of a lamp that feeds badly may often be 
confounded with a badly flaming carbon. The distinc- 
tion can readily be made after a short observation. 
The arc of a lamp that feeds badly will gradually grow 
long until it flames, the clutch will let go suddenly, the 
upper carbon will fall until it touches the lower carbon, 
and then pick up. A bad carbon may burn nicely and 
feed evenly until a bad spot in the carbon is reached, 
when the arc will suddenly become long and flame and 
smoke, due to impurities in the carbon. Instead of 
dropping, as in the former case, 
the upper carbon will feed to its 
correct position without touching 
the lower carbon. 

In a series arc lamp the shunt 
coil is used to regulate the voltage 
over the arc. With constant po- 
tential arc lamps this shunt coil 
is not needed, owing to the fact 
that the voltage over the lamp 
is practically constant. Fig. 94 
shows a diagram of an arc lamp 
for use on constant potential cir- 
cuits. The upper carbon is sup- 
ported by means of an iron yoke 
which forms a core to the two 

solenoids M M. Current entering binding post T 
passes through the windings of these two solenoids and 




FIGURE 94. 



166 ELECTRICITY FOR ENGINEERS 

then through the carbons and through the resistance 
coil R to the other terminal of the lamp. The action 
of the lamp is as follows: Current passing over the 
solenoids M M is regulated by the resistance across 
the arc. This current produces an electromagnetic 
pull on the iron core and floats, magnetically, the core 
and upper carbon. When the carbons burn away at 
the crater the distance from point to point of the car- 
bons is increased and a corresponding increase in 
resistance to the flow of the current takes place. This 
reduces the flow of current around the solenoids and 
correspondingly reduces the electromagnetic pull on 
the core; the iron core and carbon fall a slight dis- 
tance by gravity. In so doing the distance at the 
crater is decreased and the flow of current increased, 
thus increasing the flow of current around the solenoids 
and drawing up the core and carbons. In this way a 
very nice equilibrium between gravity and magnetic 
pull is maintained. It will be noticed that this lamp 
has no automatic cutout as has the constant current 
arc lamp. In a series arc lamp when the carbons are 
all consumed, the automatic cutout closes the circuit 
from the positive and negative binding posts of the 
individual arc lamp, thereby maintaining a path 
through the arc lamp over which the current can con- 
tinue to flow to supply the remaining arc lamps in the 
series circuit. 

The series arc, as its name would indicate, is the 
most simple of all lighting circuits. The lamps are 
arranged so that all the current from the positive pole 
of the dynamo goes through each, and from the last on 
the conductor leads back to the dynamo. The series 
system is more generally used where it is desired to 
illuminate a large district, as in street lighting. It is 



ELECTRICITY FOR ENGINEERS 167 

also used to some extent in store lighting, although the 
series arc is fast being replaced with the constant 
potential arc for this purpose. 

In the low tension or constant potential arc lamp the 
use of a cutout mechanism is not necessary, because 
these lamps burn singly across the system of wiring, 
where a constant potential is maintained, and hence 
when the carbons are all consumed, current simply 
ceases to flow across them. In the open arc lamp the 
potential across the crater is usually from 45 to 50 
volts, while in the inclosed arc lamp the potential 
across the crater is from 68 to 75 volts. This is due to 
the increased resistance through the crater, because of 
the peculiar nature of the gases emitted from the 
crater burning in a condition with practically no atmos- 
phere. When such an arc lamp is connected across a 
no volt circuit, the lamp contains a resistance coil in 
the mechanism box over which the current must flow 
before producing the arc, R (Fig. 94). This resistance 
coil assists to reduce the pressure from no volts down 
to the pressure required by the arc or crater. If, for 
instance, the electromotive force across the wires 
supplying current to a low tension arc lamp is no 
volts and the pressure required to maintain the arc or 
crater is 70 volts, then the resistance coil chokes down 
the electromotive force from no to 70, or 40 volts. If 
the arc consumes 4 amperes of current then the loss is 
4 (amperes) times 40 (volts), or 160 watts. This 160 
watts is lost by heat radiating to the atmosphere from 
the wire of the resistance coil. The constant potential 
lamp is usually referred to as the low tension arc lamp. 
The high tension arc lamp generally burns with the arc 
in the open air, while the low tension lamp burns with 
the arc encased in a small glass bulb so arranged as to 



168 ELECTRICITY FOR ENGINEERS 

permit the upper carbon to slide into the bulb in a 
manner that will maintain, as near as possible, a condi- 
tion whereby the arc burns in a gas containing no 
oxygen. The enclosed arc lamp has the advantage of 
burning a considerable number of hours without being 
recarboned or trimmed; but it also has the disadvantage 
that the bulb enclosing the arc turns black after burn- 
ing for some time, caused by the gases emitted from 
the arc. This renders the bulb partially opaque, 
consequently imprisoning a considerable quantity of 
useful light. Enclosed arc lamps are also operated in 
series systems, and where they are so used the objec- 
tion of loss due to the cutting down of the voltage (as 
in constant potential lamps) is overcome. Enclosed 
lamps are also operated on alternating current systems. 

The operation of the alternating arc lamp and the 
mechanism in the lamp is very similar to that of the 
direct current arc lamp, but the magnets instead of 
being constructed of solid iron, are laminated in a 
similar manner as the system of lamination explained 
in the construction of armatures. These laminated 
cores and other parts forming the magnetic circuit 
in the arc lamp are necessary to avoid eddy cur- 
rents. The crater has neither a cup shape on the 
upper carbon nor a point on the lower carbon, because 
current flows through the crater alternately positive 
and negative with each alternation. In the alternating 
arc lamp the upper and lower carbons burn away with 
almost equal rapidity, and the same quantity of light 
is projected upward as downward. 

In Fig. 95 is shown an arc lamp with case removed. 
The two upper coils are the coarsely wound series 
coils, while the two lower coils are the finely wound 
shunt coils. This lamp is adapted for an enclosed arc 



ELECTRICITY FOR ENGINEERS 



169 



bulb. The magnetically attracted cores are U shaped, 
and both cores are connected together mechanically by 
non-magnetic metal, such as brass or zinc, so that the 
magnetism set up in the shunt coils will not be affected 
by the magnetism set up by the 
series coils. This scheme is used in 
alternating current lamps, while in 
direct current lamps the cores are 
made of H shaped iron not lami- 
nated. 

In Figs. 96 to 98 are shown three 
views of series enclosed alternating 
current arc lamps of the Western 
Electric Company. 

Fig. 96. Side view of lamp, show- 
ing one series and one shunt spool, 
lever movement and adjusting 
weight. This weight is fastened 
upon a threaded rod, and the finest 
adjustment can be obtained by 
screwing the weight backward or for- 
ward. Threads can be clamped in 
position when the correct adjustment 
is obtained. 

Fig. 97. Front view of lamp, show- 
ing shunt spools, supporting resist 
ance and cutout. Note that lever 
carries no current when in normal 
working position, but that insulated bridge forms con- 
nection across two contacts, completing cutout circuit 
when in position shown in cut. 

Fig. 98. Rear view of lamp, showing series spool, 
short circuiting switch and manner of suspending dash 
pot. Note that the dash pot is inverted, allowing sucn 




figure 95 



170 



ELECTRICITY FOR ENGINEERS 



dirt as may accumulate therein to fall out rather than 
in the clash pot. 

The three cuts show the manner of suspending the 
spools and their accessibility, it being possible to 
remove any spool by simply taking out the two screws 






FIGURE 96. 



FIGURE 97. 



FIGURE 98. 



which fasten it lo the frame, and lifting it off the 
lower support. 

The carbons used in arc lamps are extremely hard 
and dense. They are made from a mixture of pow- 
dered gas house coke, ground very fine, and a liquid 
like molasses, coal tar, or some similar hydro-carbon, 
forming a stiff, homogeneous paste. This is molded 



ELECTRICITY FOR ENGINEERS 171 

into rods or pencils of required size and length, or 
other shapes, being solidified under powerful hydro- 
static pressure. The carbons are now allowed to dry, 
after which they are placed in crucibles or ovens, 
thoroughly covered with powdered carbon, either lamp- 
black or plumbago, and baked for several hours at a 
high temperature. After cooling, they are sometimes 
repeatedly treated to a soaking bath of some fluid 
hydro-carbon, alternated with baking, until the product 
is dense as possible, all pores and openings having 
been filled solid. Arc carbons are often plated with 
copper, by electrolysis, to insure better conductivity. 

It is said that one 2,000 candlepower arc lamp will 
light in open yards 20,000 sq. ft.; in railroad stations, 
14,000 sq. ft.; in foundries and machine shops, 5000 
to 2,000 sq. ft. Where good, even illumination is 
desired, it is advisable to use a greater number of 
smaller lamps evenly distributed. 



CHAPTER X 

Incandescent Lamps. As nearly every one is familiar 
with the construction of the incandescent lamp no 
detailed description will be undertaken, suffice it to 
say that the incandescent lamp comprises a carbon 
filament enclosed in a glass bulb from which the air 
has, as far as possible, been withdrawn, the carbon 
filament being soldered to the ends of small platinum 
wires entering the glass shell. Incandescent lamps can 
be burned either in series or in multiple; the multiple 
system being the most used. Series incandescent 
lamps are used to a considerable extent in the smaller 
towns for street lighting and also for the small minia- 
ture lamps burned in series on a constant potential sys- 
tem and used for decorative purposes. They are also 
used in street car lighting. 

When incandescent lamps are to be used in series, 
they should be carefully selected; there is quite a 
difference in the current consumed by different lamps, 
even of the same make, and when they are all limited 
to the same current quite a difference in candlepower 
may be noticeable. Some will be above their rated 
candlepower and others below. 

The resistance of an incandescent lamp when cold is 
very high, varying in the ordinary 16 candlepower no 
volt lamp from 600 to 1,000 ohms. When the lamp 
becomes heated, as when current is passing through it, 
the resistance reduces considerably, being in the 16 
candlepower no volt lamp about 220 ohms. 

The current required by the various incandescent 
lamps varies considerably for lamps of the same volt- 
172 



ELECTRICITY FOR ENGINEERS 173 

age and candlepovver, but a good average which can be 
used in figuring currents is y 2 ampere for a 16 candle- 
power no volt lamp and % ampere for the 220 volt 
16 candlepower lamp. The amount of power, in watts, 
consumed by a lamp is equal to the voltage multiplied 
by the current, or W = C x E. A 16 candlepower no 
volt lamp taking y 2 ampere would consume uox 
y 2 = 55 watts, while a 220 volt lamp taking y± ampere 
would consume 220x^ = 55 watts. It will thus be 
seen that while the current and voltage may vary, the 
amount of power consumed will be approximately the 
same for all 16 candlepower lamps. Lamps are rated 
at a certain number of watts per candle, the amount 
varying from 3 to 4 watts for 16 candlepower no volt 
lamps. The proper lamp to be used varies according 
to the conditions. While less power is consumed in 
a 3.1 watt lamp, the life of the lamp is comparatively 
shorter, so that the lamps will have to be renewed 
oftener. With a 4 watt lamp a greater amount of cur- 
rent is consumed, but the life of the lamp is longer. 
Another point of great importance in burning incan- 
descent lamps is the voltage. The table below shows 
what effect variation in voltage has on the candlepower 
and efficiency. 

An increase in voltage increases the candlepower. 
This increases the efficiency and shortens the life as 
follows: 

A lamp burning at — 

Normal voltage gives ioo per cent. C. P, and consumes 3.1 Watts per C. P. 

1 per cent, above normal gives 106 per cent. C. P. and consumes 3. Watts per C P. 

2 " 
3 
4 
5 
6 

A lamp burning at normal voltage should give its 



112 " " " 


2.9 


118 " " 


2,8 


125 " " 


2,7 


132 " " 


2.6 


140 " " " 


2.5 



174 



ELECTRICITY FOR ENGINEERS 



full candlepower at its rated efficiency. A 3.1 watt 
lamp burning below its voltage loses its efficiency and 
candlepower as follows: 
If burned — 

1 per cent, below normal it gives 95 per cent.C. P. and consumes 3.2 Watts per C. P. 

3-35 " " 



3 i 
3-6 

3-75 

4- 

4.6 



By referring to the table it will be seen that with the 
voltage raised 3 per cent, (on a no volt system to a 
little over 113 volts) the candlepower will increase 18 
per cent., or in other words, a 16 candlepower lamp 
would be raised to nearly 19 candlepower. At the 
same time raising the voltage will decrease the life of 
the lamp. This is shown in the following table where, 
with an increase of 6 per cent, in the voltage, the life 
of the lamp is reduced 70 per cent. A lamp at normal 
voltage has 100 per cent. life. 

The same lamp i per cent, above normal loses 18 per cent. life. 



" " " 2 " " " 


" 3o 


" 3 " 


" 44 


4 " 


" 55 


" " " s, " 


" 62 


6 " 


11 yo 



To obtain satisfactory results, the voltage should be 
kept constant at just the proper value. 

Considerable heat is generated in an incandescent 
lamp, so that as a general rule it is a bad plan to use 
paper shades which come very close to the bulb. 
Where lamps are hung so that there is a liability of 
their coming in contact with surrounding inflammable 
material, such as in warehouses and store-rooms, it is a 
good plan to enclose the lamp in a wire guard. 

The following table will prove a handy reference for 
estimating the number of lamps (8 to 50 C. P.) that 
can be run per horsepower or kilowatt. The table is 



ELECTRICITY FOR ENGINEERS 



175 



figured for theoretical values, so that the actual horse- 
power or kilowatts delivered must be used, or else 
values less than those given must be used to allow for 
loss in the lines. 



Candle-power. 


Efficiency. 


Total Watts. 


Per 

Horsepower. 


Per Kilowatt. 


8 


3-5 


28 


26.6 


35-7 


8 


4 


32 


23-3 


31.2 


16 


3 


48 


15.5 


20.8 


16 


3-i 


50 


14.9 


20 


16 


3-5 


56 


13.3 


17.8 


16 


4 


64 


ir. 6 


15.6 


?.o 


3 


60 


12.4 


16.6 


20 


3-1 


62 


12 


16. 1 


20 


3-5 


7o 


10.6 


14.2 


25 


3 


75 


9-9 


13-3 


25 


3-i 


77- 5 


9.6 


12.9 


25 


3-5 


87.5 


8-5 


11. 4 


25 


4 


100 


7 4 


10 


32 


3 


96 


7 


10.4 


32 


3-1 


99.2 


7.5 


10 


32 


3-5 


112 


6.6- 


8.9 


50 


3 


150 


4.9 


6.6 


50 


3-i 


155 


4.8 • 


6.4 


50 


3-5 


175 


4-2 


5-7 



The first column gives the candlepower. The second 
column gives the number of watts consumed for each 
single candlepower obtained, and is called the effi- 
ciency of the lamp. Multiply the total candlepower 
by the efficiency and you get the total number of watts 
consumed by the lamp. The fourth column shows the 
number of lamps per 746 watts, and the last column 
the number of lamps per 1,000 watts. 

The current and watts consumed by 110 volt lamps 

of the different candlepowers are approximately given 

below. 

4 candlepower o. 18 amperes, 20 watts 

8 " .0.29 " 32 " 

16 " 0.5 " 55 " 

32 1.0 " no " 



176 ELECTRICITY FOR ENGINEERS 

The light given off by an incandescent lamp varies 
according to the position from which it is viewed. In 
some makes of lamps most of the light is given off 
directly downward, while in other lamps the maximum 
light is given off in a horizontal direction. The best 
lamp to use must be determined by the location of the 
lamp and the place where the light is required. By 
the use of suitable reflectors or shades the light can be 
thrown in any direction desired. A 16 candlepower 
lamp if placed seven feet above the floor will light up 
a floor space of ioo sq. ft., providing the walls are of a 
light color. If the walls are of a dull color, or if a 
bright illumination is desired more lamps should be 
used. Glass globes placed over the lamps reduce the 
light to a considerable extent, as is shown in the fol- 
lowing table: 

Clear glass 10 per cent. 

Holophane 12 " 

Opaline 20 to 40 " 

Ground . 25 to 30 " 

Opal 25 to 60 " 



CHAPTER XI 

The Nernst Lamp. Very recently a new type of elec- 
tric lamp has been introduced which has a few charac- 
teristics of the arc lamp and many of the characteristics 
of the incandescent lamp. It is a lamp that can be 
successfully operated only on alternating currents. 
That part of the lamp from which the light is emitted 
is called the glower. The glower performs about the 
same functions as does the filament in an incandescent 
lamp. 

In Fig. 99 a diagram of a six glower lamp is shown. 
The six glowers are shown at 6. These glowers are in 
the shape of small rods and are composed of an oxid r. 
which, at the normal temperature, is of very high 
resistance, the resistance being so high that practically 
no current can flow through them. When these rods 
become heated, the resistance reduces considerably, so 
that they will conduct current. The heaters which are 
composed of a considerable length of fine platinum 
wire embedded in porcelain, are shown at 5. The 
action of the lamp is as follows: Current enters at 1, 
and being unable to flow over the glowers on account 
of their high resistance, passes to the cutout 4', then 
through the platinum wire of the heaters back to the 
other side of the cutout 4. As the platinum wire in 
the heaters becomes heated, the glowers, which are 
placed directly below them, also heat up and in time 
their resistance becomes so reduced that current will 
pass through them. The current will now pass through 
the glowers to what is known as the ballast, 7. This 
177 



178 



ELECTRICITY FOR ENGINEERS 



ballast is composed of fine iron wire and its purpose is 
to steady the current through the glower. From the 
fact that iron wire increases in resistance with increase 
of current, this wire acts as a regulator, tending to cut 




FIGURE 99. 



down any fluctuations in the current strength. It will 
be noticed that there is a separate ballast for each 
glower. From the ballast the current flows around the 
coil of wire 3. Inside of this coil is an iron core which 



ELECTRICITY FOR ENGINEERS 



179 



moves up and down, and connected to the lower end 
of this core are the cutouts 4,4'. As the glower 
becomes heated, more current is sent around this coii, 
until it becomes of such strength that the core is 
drawn in, thus opening the cutouts. All of the cur- 
rent will now flow through the glowers. The Nernst 
lamp does not operate successfully on direct current, 





FIGURE 100. 



due to the blackening of the glower caused by decom- 
position of the platinum contacts with which they are 
connected. These lamps are made in sizes of from 1 
to 30 glowers, and they consume about 88 watts per 
glower. The light resembles very closely the light 
from a Welsbach gas burner, although the green tinge 
of the Welsbach is not present. 



180 ELECTRICITY FOR ENGINEERS 

In Fig. ioo is shown the single glower lamp 
assembled, which can be inserted in an ordinary Edi- 
son socket. 

In Fig. 101 the six glower lamp, with dome attached, 
is shown. 



CHAPTER XII 

Line Testing. In the operation of electric light and 
power circuits three principal causes of trouble are 
continually encountered. These are the open circuit, 
the short circuit, the ground, and also combinations of 
these, as there is nothing which prevents the existence 
of all three defects on any line at the same time. In 
order to study these properly, let us refer to Fig. 102, 
which shows an ordinary incandescent circuit equipped 
with the necessary cutout and a switch. 

An open circuit may be caused by poor contact, or 

H F 







FIGURE 102. 



failure to make any contact at all, of the fuse. If this 
is the cause, the light can be made to burn by connect- 
ing the fuse terminals A and B or C and D by means 
of short pieces of wire. Such wire must, however, be 
used only for an instant to make sure of the trouble, 
and proper fuses must then be provided. Another 
method of locating an open circuit in the fuse consists 
of moistening the finger tips and placing the tips of 
two fingers of the same hand on B and D. If the fuses 
are in order, a slight shock will be felt; this method is 
applicable only on low voltage systems and must never 
be used where the voltage exceeds 250. 
181 



182 ELECTRICITY FOR ENGINEERS 

If the fuses are found all right, the next place to look 
for the cause of an open circuit is at the switch. The 
contact points of switches are often so badly burned 
or covered with dirt and grease that they do not make 
proper connection and hence the lights will not burn. 

The switch can be tested with the fingers just as we 
tested the cutout, and if the shock is felt the line is 
all right to this point. In testing the switch, be sure 
you test at the proper point (i and 2) in the figure 
which shows a switch, the blades of which cross. 
Some switches make connection straight along without 
crossing. In testing with a wire, as shown above, be 
very careful not to connect the points 1 and 2 at the 
switch, or you will have a short circuit. 

If the line is found alive at the far side (points 1 and 
2) of the switch shown, and still the lights do not burn, 
it is quite likely that there is a broken wire between 
the switch and the lamps. This break in the wire is 
not always visible, as often the wire is entirely con- 
cealed, and even when the wire is in plain view, the 
break may extend only to the copper and leave the 
outer insulation apparently perfect. 

If we are dealing with concealed wires that appear 
only where the lights are connected, we must first 
examine the connections at all such places and see 
whether they are in good order. If we find nothing 
wrong there we may proceed to locate our open circuit 
(which we shall assume to be at E) by the following 
method: In place of one of the fuses AB or CD, con- 
nect any incandescent lamp (if plug cutouts are used 
the lamp can be screwed in instead of the plug). Now 
connect a wire from 1 or 2 of the switch to 3 or 4 of 
the nearest lamp. 

If we happen to connect our wire from 1 to 4 we 



ELECTRICITY FOR ENGINEERS 183 

shall make a short circuit and the lamp at the cutout 
will burn at full candlepower, but none of the other 
lamps will burn at all. Now disconnect the test wire 
from 4 and connect it at 3; if the broken wire is at E, 
as we have assumed, all the lights will now burn in 
series with the lamp in the cutout. If there are but 
few lights connected in the circuit, this lamp will burn 
at about half candlepower; if there are many lamps 
connected it will come nearly to full candlepower, and 
the lamps in the circuit will show nothing. 

If instead of an open circuit the cause of our trouble 
is a short circuit, it will first make itself evident by a 
burned out fuse in the cutout at AB or CD. 

A little experience will soon enable one to judge 
whether a burned out fuse is due to an overload or a 
short circuit; the damage to terminals and the evi- 
dence of burning will be much greater from a "short" 
than from a slight overload. 

Often the current that "blows" the fuse will also 
burn out the wire which caused the "short," so that 
the line will seem perfectly clear when a new fuse is 
inserted. 

If an inspection of the wires and apparatus does not 
reveal the location of the trouble, we may fuse up one 
side of the circuit and connect an incandescent lamp 
in place of the other fuse. If the "short" is still on, 
the lamp will burn at full candle power. 

A short circuit may consist of anything of low elec- 
trical resistance that brings the wires of opposite 
polarity into electrical connection with each other. 
Thus, if the two points, F and G, although several 
hundred feet or even yards apart, were in connection 
with gas or water piping of low electrical resistance, 
all current would flow through the piping from F to G, 



184 ELECTRICITY FOR ENGINEERS 

and there would be none to flow through the lamps. 
Short circuits are also often caused by small wires in- 
side of sockets or fixtures coming in improper contact. 
In one instance a short circuit which caused a search 
of several hours was finally located in the butt of an 
Edison base lamp, the center contact piece of which 
had been put on crooked in such a manner that when 
the lamp was screwed into its socket this center piece 
made connection with opposite poles within the socket. 

If a careful examination does not reveal the "short" 
it will be necessary to cut the wires, say at H; if this 
clears the line so that all lamps nearer the cutout than 
H burn, the trouble must be beyond H; if not, the line 
must be cut again nearer the cutout until finally the 
exact location of the trouble is found. 

Any connection of any part of an electrical circuit to 
earth is called a "ground," and wires so connected are 
said to be grounded. One ground on a system will 
not necessarily do much harm or interfere with the 
operation of the system. It will, however, greatly 
increase the probability of electric shocks to people 
coming in contact with any part of the wiring. Also, 
if there is a ground on one side of a system, the 
appearance of a second ground on the other side of the 
system will be equal to a short circuit, if both are of 
low resistance, and probably cause the burning out of 
fuses or wires. 

If a ground is of high resistance, it may merely 
waste energy through leakage of current; or it may 
cause slow destruction of a wire or sometimes a gas or 
water pipe by electrolytic action. Aside from direct 
contact with metal parts of buildings, the most prolific 
cause of grounds is found in dampness. 

Grounds may be located by means of the Wheatstone 



ELECTRICITY FOR ENGINEERS 



185 



bridge, magneto or a common bell and battery. After 
removing the fuses from the grounded part of the 
system, connect one side of the apparatus to a good 
ground, such as a water pipe, and the other side to the 
system. Proceed in the same way as explained for 
short circuits; that is, cut the lines until the ground is 
located, or the line shows clear. Where the wiring is 
concealed and there are a number of switches control- 
ling chandeliers, grounds can very often be located by 
switching off one fixture at a time, for when the 
grounded fixture is switched off the line will show 
clear. 

To facilitate the discovery of grounds as soon as they 
come on, most switchboards are equipped with ground 
detectors of some kind. 

The cheapest and easiest to install of these consists 
of two lamps in series, as shown in Fig. 103. So long 



~3 



LSi 



+ 



£ 



2L 



FIGURE 103. 



as both sides of the system are clear of grounds, the 
lamps will both burn at equal candlepower (rather dim) 
no matter whether the buttom C be pressed or not. 
But should a ground come on the 4- wire, say at B, and 
the button C be then pressed, the lamp 2. will be 
deprived of current and lamp I will burn at full candle- 
power. In such a case the current passes from the 
-f wire to the ground B, through the ground to C, 



186 



ELECTRICITY FOR ENGINEERS 



button C and lamp I to the — wire. Should a ground 
come at A, lamp I would be cut out and 2 womd 






pq 



w 



OO-i 




DO- 1 



DP 



m> 



* + 



burn at full candlepower. The great disadvantage of 
the lamp ground detector lies in the fact that it is not 
very sensitive; that is, unless the ground is of quite 



ELECTRICITY FOR ENGINEERS 



187 



low resistance the difference in the brilliancy of the 
lamps will hardly be noticeable. 

A much more satisfactory arrangement is that shown 
in Fig. 104, where a voltmeter is connected for that 
purpose. With the two single pole switches A and B 
in the position shown, the voltmeter indicates the 
pressure of the dynamo; if B is thrown over, the 
current from the 4- wire passes through the voltmeter 
to the ground, and if there is a ground on the - wire it 
will indicate it. If B is thrown back and A over, a 



_$! S$- 



©. 



FIGURE 105. 

ground on the + wire will be indicated. If the system 
is perfectly clear, the voltmeter will indicate nothing 
with either one of the switches thrown over. This test 
of lines and circuits should be quite frequently made. 

Testing Efficiency of Dynamos and Motors. The simplest 
means of testing the efficiency of motors is shown in 
Fig. 105. 

This is known as the Prony brake, and consists of a 
pair of clamps arranged for thumb screws and fastened 
to the pulley of the motor, and a set of scales. 

We will assume that we are testing the efficiency of 



188 ELECTRICITY FOR ENGINEERS 

a motor. We will arrange the clamps over the pulley- 
as shown in the figure and on the long end of the 
clamp w r e will arrange a bolt, from which we may 
impart the pressure obtained to the platform of a pair 
of scales. In the circuit supplying the motor with cur- 
rent we will connect an amperemeter and a voltmeter. 
We will now start the motor and press down on the 
clamps by means of the thumb screw, until the 
mechanical energy expended is sufficiently high to 
cause the desired consumption of current shown by the 
amperemeter at the pressure shown by the voltmeter. 
With a tachometer or speed indicator we will find the 
number of revolutions of the motor per minute. When 
this has been done, we will take the weights on the 
scales and balance the pressure brought down on the 
platform. Now stop the motor. The weight indi- 
cated by the scales is that weight which the motor 
would have revolved through a circle, the radius, or 
half the diameter of which is the distance from the 
center of the motor shaft to the center of the bolt 
pressing on the scale platform, Fig. 105. To find the 
horsepower exerted, multiply the distance between the 
bolt and the armature shaft by 2.. This will be the 
diameter of the circle described. Multiply this by 
3.1416. This will be the circumference of the circle 
described. Multiply this by the number of pounds 
indicated by the scales, multiply this by the number of 
revolutions per minute, and divide the answer by 
33,000. 

Suppose your amperemeter registered 50.9 amperes 
and your voltmeter registered no volts. This would 
be 50.9 x no = 5,599 watts consumed. Divided by 746 
watts, the electrical horsepower would be 7^ horse- 
power consumed. 



ELECTRICITY FOR ENGINEERS 189 

Suppose the dynamometer proved that you obtained 
six actual mechanical horsepower. Then 6 divided by 
7^ would be 80 per cent, efficiency which the motor 
would have for changing electrical energy into mechan- 
ical energy. 

To test the efficiency of a dynamo we must first find 
how much power is being delivered to it by the engine. 
This is done in the usual manner by means of the indi- 
cator, etc. Having obtained this, it is simply neces- 
sary to connect an ammeter and voltmeter and, taking 
simultaneous readings of both, find the power given 
out by the dynamo by multiplying together the volts 
and amperes. 

As an example, suppose we have found that our 
engine is delivering 40 H. P. while we are obtaining 
from our dynamo 200 amperes at no volts pressure. 
200 x no divided by 746 will give us the electrical 
energy we are receiving; in this case a trifle less than 
29.5 H. P. To find the efficiency of the dynamo we 
divide the power received from the dynamo by that 
delivered to it by the engine, 29.5 divided by 40 equals 
.737, which is the efficiency of this dynamo. When 
testing dynamos it is usual to provide an artificial load 
which can be kept constant. Large metal plates, 
preferably copper, are connected to the positive and 
negative mains of the dynamo and immersed in a 
barrel of water. The quantity of current that will flow 
from one plate to the other can be regulated by dis- 
solving more or less salt in the water and by immers- 
ing the plates more or less and also by bringing them 
closer together. The greater the surface of the plates 
immersed in the water and the nearer they are brought 
together, the greater will be. the current. Be very care- 
ful and do not let the plates touch each other. Before 



190 



ELECTRICITY FOR ENGINEERS 



accepting a new dynamo a test run of twenty-four 
hours at full load is usually made and the water rheo- 
stat need be used only to keep the load constant when 
lights are switched on or off. 

Photometer. The amount of light given off by an 
incandescent lamp is measured in candlepower. To 
determine the candlepower of a lamp, an appaiatus 
known as the photometer is used. Fig. 106 shows a 
diagram of what is known as the Bunsen photometer. 
S is a scale divided into inches, meters, or any suitable 
divisions, at one end of which is placed a standard 
lamp and at the other end the lamp to be measured. 




FIGURE 106. 



A small screen, made of white paper having a grease 
spot in the center, is mounted on a stand so that it can 
be moved along the scale. To operate the instrument, 
move the screen to such a point that the grease spot 
becomes invisible from either side. The two candle- 
powers are now to each other as the squares of their 
distances from the screen. For instance, suppose the 
lamp A is a standard 16 candlepower lamp and at the 
point where the grease spot is invisible the distance 
from B to the screen is 20 in., and from A to the 
screen 40 in., then B is to A as 20 squared is to 40 
squared, or as 400 is to 1,600 or one-fourth as 
great; therefore B is a 4 candlepower lamp. Care must 



ELECTRICITY FOR ENGINEERS 



191 



be taken that the two lamps are burning at just the 
proper voltage, otherwise the comparison will not be 
accurate. Instruments of the kind just described are 
made in a variety of different patterns, but their prin- 
ciple remains the same. Candlepowers may also be 
compared by a method known as Rumford's.' Take a 
pencil or other opaque rod and place it in front of a 
white piece of paper or light-colored wall. Now place 




in front of it, but separated so that there will be two 
separate shadows cast, the two lamps to be compared. 
By moving one of the lamps away from, or closer to, 
the screen, at some point the two shadows will become 
of the same density. Now measure the distances of the 
two lamps from the screen, and their candlepowers 
will be to each other as the squares of the distances; 
(Fig. 107). 



192 ELECTRICITY FOR ENGINEERS 

If the current consumed by a lamp and the voltage 
maintained at its terminals are measured by an amme- 
ter and voltmeter, as shown in Fig. 106, we need only 
find the watts (current times volts) and divide by the 
candlepower to find the efficiency of the lamp. If, for 
instance, the 4 candlepower lamp B is taking J ampere 
at no volts, we have 18^3 watts expended on it; this 
divided by the candlepower 4 shows an efficiency of 
4 T \ watts per candle. 



CHAPTER XIII 

Storage Batteries. The storage battery is often 
referred to as an accumulator. An accumulator is an 
appliance for storing electricity. It depends upon the 
chemical changes undergone by certain substances 
when subjected to the action of an electric current. 
Strictly speaking, it is not correct to say that electri- 
city is stored in an accumulator, although as far as 
external results is concerned such appears to be the 
case. What it really does is this: The current flowing 
into the accumulator produces a gradual chemical 
change or decomposition of the active elements of 
which the battery is constructed. This change con- 
tinues to take place as long as the charging current is 
applied. This is known as electrolytic action. As soon 
as the current ceases, so also does the chemical decom- 
position of the elements cease, and if the terminals be 
then connected by a wire, a reversal of the chemical 
process commences. Particles gradually reform them- 
selves into original chemical combinations, and by so 
doing produce a current of electricity which flows in 
opposite direction to that originally used for charging. 

An early form of accumulator, though more of 
experimental than practical interest, was Grove's gas 
battery. This was composed of a series of cells, each 
cell comprising two tubes, closed at the upper ends, 
and dipping down into a glass jar containing acidu- 
lated water. Each tube had a platinum wire fused into 
the closed end, from which a strip of platinum foil 
extended downwards into the liquid. The outer ends 
193 



194 ELECTRICITY FOR ENGINEERS 

of the platinum wires were provided with terminals, by 
means of which several of these cells were connected 
together. A charging current was then applied and 
resulted in the gradual decomposition of the water in 
the various glass jars. Hydrogen collected on one of 
the platinum plates in each of the cells and oxygen on 
the other. If after a short time the charging source 
was disconnected from the wires joined to the outer 
terminals of the cells and a galvanometer substituted, 
it was found that a current would then flow in the 
reverse direction until all the separated hydrogen and 
oxygen gases had recombined to form water again. 

From a practical point of view the gas battery was 
deficient, inasmuch as it would only supply current for 
a very short-time, and several workers set themselves 
the task of contriving an arrangement to obviate this 
defect. The most successful of these early workers 
was Plante, and he found in the course of his experi- 
ments that the best results were to be obtained by 
using lead plates or electrodes in a dilute solution of 
sulphuric acid. He made a cell by taking two long 
strips of sheet lead, placed one over the other with 
pieces of insulating material between, and coiling 
these up into spiral form. These plates were provided 
with separate terminals and were placed in a jar con- 
taining a solution of sulphuric acid. The action of the 
charging current was to decompose the water in the 
solution, the oxygen combining with the metal of the 
positive plate and thus forming peroxide of lead, 
whereas the hydrogen was simply deposited on the 
negative plate and there remained in gaseous form. 
On discontinuing the charging current, the hydrogen 
combined with the oxygen in the solution to form 
water again, while the peroxide of lead was deoxidized, 



ELECTRICITY FOR ENGINEERS 195 

the lead remaining on the surface of the plate as 
spongy lead, and the oxygen reentered the solution to 
compensate for the oxygen which was extracted there- 
from by the hydrogen in forming water. Plante found 
that this method of construction enabled him to get an 
electromotive force of from 2 to 2.5 volts, as against 
1.47 volts given by Grove's gas battery. 

Plante's experiments did not, however, terminate 
with this achievement, and he next introduced a 
method for considerably increasing the available 
metallic surface of the electrodes. This plan is known 
as "forming" the plates, and consists of repeating for 
a considerable time the following series of operations: 
(1) charge the accumulator, (2) discharge ditto, (3) 
recharge, but with the charging current entering in the 
reverse direction, (4) again discharge. This series of 
reversals in charging and discharging, if kept up for 
several days, has the effect of causing the lead plates 
to become very porous or spongy in character, and, 
therefore, by reason of the additional surface of con- 
tact between electrolyte and electrode thus provided, 
enables the cell to retain a much greater charge than 
it would otherwise. 

It is not difficult to see that this work of forming 
is of a somewhat tedious and expensive character, and 
with the object of reducing this process to a minimum, 
another inventor, Faure, conceived the idea of using 
plates coated with a paste of lead-oxide, a plan which 
made it possible to use an accumulator with success 
after being charged only two or three times. When first 
introduced, some difficulty was found in making the 
lead-oxide paste adhere properly to the plates, and 
various means were devised to overcome this drawback. 
Scratching and indenting the lead plates was tried, 



196 ELECTRICITY FOR ENGINEERS 

but this was ultimately superseded by the plan of 
making perforated plates in the form of grids, the 
paste being pressed into the perforations. With vari- 
ous slight modifications, in the shape of perforations, 
this device has been found to answer exceedingly well, 
and is now very generally adopted. 

When an accumulator is freshly charged, it would be 
found to have an electromotive force of about 2.25 to 
2.5 volts, but after being used a short time this falls to 
about 2 volts, at which figure it remains until the cell 
is nearly exhausted. For many purposes, however, a 
higher voltage than this is required, and it then 
becomes necessary to have several cells joined in 
series, so as to give a total voltage equal to the 
number of cells multiplied by 2. Thus 20 cells of 2 
volts each, if joined in series, would give an electro- 
motive force of 40 volts; 50 cells would give 100 volts, 
and so on. 

The quantity of current which a cell will accumulate 
or store depends upon the area of its plates; thedarger 
the plates the greater the capacity of the cell, and the 
higher the permissible rate of discharge. As it is not 
always convenient to use very large plates where great 
capacity is required, the same result may be obtained 
by using a number of small plates to increase the 
available plate surface, but in such cases the plates 
must be connected in parallel. That is, the positive 
plates must all be connected to one terminal, and the 
negative plates all to the other terminal, thus forming 
practically two plates divided into a number of 
branches. 

The capacity of an accumulator is usually measured 
in ampere hours. Thus an accumulator which will 
discharge a current of ten amperes for one hour, or of 



ELECTRICITY FOR ENGINEERS 



197 



five amperes for two hours, or of one ampere for ten 
hours, is said to have a capacity of ten ampere hours. 
As a general rule, it maybe estimated that an accumu- 
lator has a capacity of six ampere hours for each 
square foot of positive plate surface. 

For charging storage batteries the shunt dynamo is 
generally used, and the voltage must be kept as nearly 
constant as possible. Fig. 108 shows a very simple 
installation where the battery is intended to be charged 
during the running time of the dynamo and to carry 
the lights during such time as the dynamo is not in 




FIGURE 108. 



action. The ammeter A, in the battery line, should 
be of a kind which indicates the direction of the cur- 
rent passing through it. The rheostat R is used to 
regulate the charging current and the voltmeter V is 
connected so that either the voltage of the dynamo or 
the battery may be taken. In addition to this volt- 
meter a low reading meter should also be provided to 
test single cells. An automatic circuit breaker is also 
often provided to open the circuit should the current 
through it flow in the wrong direction. Should, for 
any reason, the voltage of the dynamo fall below that 



198 ELECTRICITY FOR ENGINEERS 

of the battery while charging, the battery would begin 
to discharge through the dynamo. Where it is import- 
ant that the voltage supplied by the battery shall be 
at the same voltage as that supplied by the dynamo, a 
"booster" is employed to help charge the battery. 
Such a booster increases the electromotive force at 
the terminals of the battery sufficient to allow it to be 
charged to the full pressure of the dynamo. In setting 
up and charging storage batteries, detailed instructions 
should be obtained from the makers and rigidly 
followed. 



CHAPTER XIV 

Electrolysis. Electrolysis is chemical decomposition 
effected by means of the flow of an electric current. 
Bydectrolytic action it is possible to deposit metals, 
such as gold, silver, nickel, etc., over the exterior 
surface of other metals. This process is ordinarily 
called nickel plating, gold plating, etc., and is carried 
on by means of tanks in which there are liquids hold- 
ing in solution some of the various metallic salts. By 
placing over these tanks a bar or number of bars made 
of brass or copper, we may hang articles from these 
bars by means of wires, so that they are submerged in 
the' solution. Now by using a dynamo whose output 
is low in pressure or electromotive force and high in 
quantity or amperes, and connecting the positive or 
outgoing terminal of this machine to a piece of metal, 
such as copper, nickel, gold, or silver, and submerging 
this metal in the liquid contained in the tank, the flow 
of current from this piece of gold or silver into the 
liquid or bath will carry with it, by electrolysis or 
electrolytic action, some of this gold or silver and 
deposit it on the articles suspended in the liquid, from 
the brass or copper bars to which the negative terminal 
of the plating dynamo is connected. The use of the bath 
containing metallic salts reduces the resistance from 
the metal to be deposited on the articles that are to be 
plated, which are the negative electrodes. This effects 
an equal deposit of metal over the entire surfaces 
being subjected to the electrolytic or plating action. 

Where it is desired to cover such metals as steel or 
199 



200 ELECTRICITY FOR ENGINEERS 

iron with silver or gold, it becomes necessary to subject 
the articles to De plated to what is called a striking 
bath. 'This striking bath consists of a system of elec- 
trolytic action as above described, where copper is first 
deposited over the surfaces of iron or steel. The more 
precious metals will distribute themselves over this 
copper surface more uniformly and in a finer grained 
manner than if the article had not been copper plated 
first. After the plated article has had sufficient metal 
deposited on its surface, it is put through a buffing and 
polishing process for its final finish. 

Electrolysis has also been applied where it is desired 
to reclaim the precious metals from ores without smelt- 
ing them. This method consists of immersing the ore 
in tanks filled with a solution. The ore receives cur- 
rent from the positive element of a dynamo through 
the liquid solution, and the metal in the ore is depos- 
ited on the negative plate in the vat, which is con- 
nected to the negative terminal of the dynamo. Thus 
by employing a process similar to electro plating it is 
possible to extract the metal from the ores in almost 
its pure state from the negative plate. The solution 
mentioned is water in which various kinds of metallic 
salts have been dissolved which bear a chemical rela- 
tion to the metals to be extracted. 

This short description will assist in explaining how 
electrolytic action takes place in water and gas pipes 
buried under the surface of the ground, when, for 
instance, electric railroads, operated in the vicinity 
are not properly constructed. In the construction of 
an electric street railroad or trolley line the generators 
are connected to the trolley wires usually at the posi- 
tive terminals of the dynamos. 

The current passes from the trolley line through the 



ELECTRICITY FOR ENGINEERS 201 

.car to the rails and back to the negative pole of the 
dynamo. If the rails are not of sufficient carrying 
capacity, or if there is a pipe line of better carrying 
capacity near the rails, it is quite certain that some of 
the current will be carried by the pipes. Wherever 
the current leaves a pipe it carries some of the metal 
with it, and if there is much current a hole will soon 
be eaten into the pipe. As the pipes are mostly 
covered with rust, which is a partial insulator, the 
current will be most likely to enter and leave the pipe 
at some point which is comparatively bright and the 
electrolytic action will be concentrated at such points. 

Heating by Electricity. The electric heater is simply 
a coil of wire through which enough current is caused 
to flow to produce quite an appreciable amount of 
heat. In the use of resistance coils for nearly all elec- 
trical purposes the function of the resistance coil is to 
cut down the flow of current required at some point, as 
for instance, where a resistance coil is used as a start- 
ing box on a motor. The flow of current across or 
through such a coil or coils, will produce heat, and 
shows one way in, which electric power can be con- 
verted into heat. Another instance, if a contact is 
poorly made, the resistance to the flow of current 
offered by this contact produces heat and a consequent 
loss of watts. The voltaic arc in an arc lamp is 
another instance where resistance to the flow of current 
is interposed in the circuit and consequently produces 
heat. 

The incandescent lamp is another instance where 
resistance is the cause of the production of heat, but, 
of course, in both the arc and incandescent light, the 
result desired is a maximum amount of light with a 
minimum amount of heat. 



202 ELECTRICITY FOR ENGINEERS 

If we were to construct a coil of small wire, whose 
total resistance would be the. same as that of another 
coil of large wire, it would be found that the coil of 
small wire would contain much less wire than the coil 
of large wire, both resistances being the same in ohms. 
Now if both these coils were connected across a circuit, 
we will say of no volts, the same amount of current 
would flow over both the coils, because their resist- 
ances are alike, but the smaller coil would get quite 
hot, while the larger coil would perhaps be just 
slightly warmed. The number or quantity of heat 
units gi en out by both coils are the same. The sur- 
face from which these heat units pass out into the 
atmosphere is much less in the smaller coil than in the 
large one, hence the smaller coil gets quite hot, some- 
times even red hot. If we were to permit current to 
flow over this small coil and maintain its temperature 
at a low red heat, it would in time become oxidized by 
the chemical action of the oxygen in the air. To pre- 
vent this oxidization we may imbed this small coil in 
a porcelain cement, and after it has been properly 
imbedded in this cement we will put the entire coil 
and cement through a baking process, making the 
cement quite hard and sealing the wire coil from the 
influence of the oxygen in the atmosphere. Then 
we can take this coil so constructed and produce 
heat in a flat iron, or in a stove, in a curling iron, 
soldering iron, and in fact anywhere. The coil being 
so hermetically se-aled it can also be used in chafing- 
dishes, tea kettles, water urns, glue pots, etc. The 
principle of producing heat by electricity remains the 
same no matter where or how it is applied, the only 
difference necessary being in the form given to the 
heater coils. 



ELECTRICITY FOR ENGINEERS 203 

Heating by electricity is quite an expensive and 
uneconomical proposition, and an idea can be obtained 
as to the quantity of current necessary to do electric 
heating, when we consider that in very cold weather it 
requires nearly as much power to operate the heaters 
in a street car system as it does to propel the cars. 



CHAPTER XV 

Lightning Arresters. Lightning arresters are needed 
on overhead, outdoor lines only. The simplest form 
of lightning arrester consists of two bare metal plates 
set very close together, but under no circumstances 
allowed to touch each other. (See Fig. 109.) One of 
these plates is connected to the overhead line and the 
other to the ground. 

A sudden flow of current meets with an enormous 
opposition when it encounters the coils of a large 
electro magnet. Although the resistance of the air 
space between the two plates forming the lightning 
arrester may be several millions of ohms, it is far 
easier for the current to jump this air space in such a 
very short time as is taken up by a lightning-discharge 
than it would be to force its way around the coils of 
the magnet. The reason for this is, that a current of 
electricity flowing through the coils of an electro mag- 
net creates magnetism or lines of force. These lines 
of force cut through the coils on the magn-et and in 
that way tend to produce a counter current, or counter 
electromotive force, which, for a very short time, is 
almost equal to the electromotive force creating it. 
Were the current flow to continue for any appreciable 
time this counter electromotive force would disappear 
entirely as soon as the magnetism reached its final 
strength. 

In order, therefore, to facilitate as much as possible 
a lightning discharge towards the ground and away from 
the machinery and buildings, the wires leading from 
204 



ELECTRICITY FOR ENGINEERS 



205 



the arresters to the earth should be run in as straight a 
line as possible and be kept well separated from metal 
parts, especially iron, of the building. Under no cir- 



TO 

LINE 



WWVWVWWVWV 
AAA/NAAAAAAAAAAAA 



TO 
GROUND 



FIGURE 109. 

cumstances should the ground wire be run in an iron 
pipe, nor should lead covered wires be used. 

With the simple lightning arrester shown above there 
is great liability of the current from the dynamo fol- 
lowing the arc caused by the lightning discharge to 



200 



ELECTRICITY FOR ENGINEERS 



ground, and, as there must be two arresters, one on eauh 
side of the dynamo, this amounts almost to a short 
circuit and is very likely to put the dynamo out of 
service. Should such an arc continue for a few min- 
utes, it may fuse the plates of the arrester. The arc 
can readily be extinguished by blowing it out or caus- 
ing a strong blast of air to strike it. 

To prevent trouble of this kind the Thomson light- 




FIGURE 110. 



ning arrester, shown in Fig. no, was devised. This 
consists of the two diverging metal plates shown at 
the top of the figure, one of which is connected to the 
earth and the other to the line to be protected and an 
electro magnet, as shown. The current from the 
dynamo traverses the coils of the electro magnets. 
The action is as follows: When a lightning discharge 
through the arrester takes place, it forms an arc 



ELECTRICITY FOR ENGINEERS £()7 

between the lower points of the plates above the mag- 
nets. These plates are very close together at the 
bottom. Now the electric arc is always strongly 
repulsed by a magnet, and hence the arc formed is 
forced upward where the plates diverge, and the space 
becomes too great for it to be maintained and it is 
then broken. The arc is virtually blown out by the 
magnetism. 



22 .500 



